Adding upstream version 115.8.0esr.upstream/115.8.0esr

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

10 files changed, 2464 insertions, 0 deletions

diff --git a/toolkit/components/telemetry/tests/gtest/TelemetryFixture.cpp b/toolkit/components/telemetry/tests/gtest/TelemetryFixture.cpp
new file mode 100644
index 0000000000..35742654f6
--- /dev/null
+++ b/toolkit/components/telemetry/tests/gtest/TelemetryFixture.cpp
@@ -0,0 +1,28 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+
+#include "TelemetryFixture.h"
+#include "mozilla/dom/SimpleGlobalObject.h"
+
+using namespace mozilla;
+
+void TelemetryTestFixture::SetUp() {
+  mTelemetry = do_GetService("@mozilla.org/base/telemetry;1");
+
+  mCleanGlobal = dom::SimpleGlobalObject::Create(
+      dom::SimpleGlobalObject::GlobalType::BindingDetail);
+
+  // The test must fail if we failed getting the global.
+  ASSERT_NE(mCleanGlobal, nullptr)
+      << "SimpleGlobalObject must return a valid global object.";
+}
+
+AutoJSContextWithGlobal::AutoJSContextWithGlobal(JSObject* aGlobalObject)
+    : mCx(nullptr) {
+  // The JS API must initialize correctly.
+  JS::Rooted<JSObject*> globalObject(dom::RootingCx(), aGlobalObject);
+  MOZ_ALWAYS_TRUE(mJsAPI.Init(globalObject));
+}
+
+JSContext* AutoJSContextWithGlobal::GetJSContext() const { return mJsAPI.cx(); }
diff --git a/toolkit/components/telemetry/tests/gtest/TelemetryFixture.h b/toolkit/components/telemetry/tests/gtest/TelemetryFixture.h
new file mode 100644
index 0000000000..f89aecf6a8
--- /dev/null
+++ b/toolkit/components/telemetry/tests/gtest/TelemetryFixture.h
@@ -0,0 +1,39 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+
+#ifndef TelemetryFixture_h_
+#define TelemetryFixture_h_
+
+#include "gtest/gtest.h"
+#include "mozilla/CycleCollectedJSContext.h"
+#include "mozilla/dom/ScriptSettings.h"
+#include "nsITelemetry.h"
+
+class TelemetryTestFixture : public ::testing::Test {
+ protected:
+  TelemetryTestFixture() : mCleanGlobal(nullptr) {}
+  virtual void SetUp();
+
+  JSObject* mCleanGlobal;
+
+  nsCOMPtr<nsITelemetry> mTelemetry;
+};
+
+// AutoJSAPI is annotated with MOZ_STACK_CLASS and thus cannot be
+// used as a member of TelemetryTestFixture, since gtest instantiates
+// that on the heap. To work around the problem, use the following class
+// at the beginning of each Telemetry test.
+// Note: this is very similar to AutoJSContext, but it allows to pass a
+// global JS object in.
+class MOZ_RAII AutoJSContextWithGlobal {
+ public:
+  explicit AutoJSContextWithGlobal(JSObject* aGlobalObject);
+  JSContext* GetJSContext() const;
+
+ protected:
+  mozilla::dom::AutoJSAPI mJsAPI;
+  JSContext* mCx;
+};
+
+#endif  // TelemetryFixture_h_
diff --git a/toolkit/components/telemetry/tests/gtest/TelemetryTestHelpers.cpp b/toolkit/components/telemetry/tests/gtest/TelemetryTestHelpers.cpp
new file mode 100644
index 0000000000..1848052c2e
--- /dev/null
+++ b/toolkit/components/telemetry/tests/gtest/TelemetryTestHelpers.cpp
@@ -0,0 +1,372 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+
+#include "TelemetryTestHelpers.h"
+
+#include "core/TelemetryCommon.h"
+#include "gtest/gtest.h"
+#include "js/Array.h"               // JS::GetArrayLength, JS::IsArrayObject
+#include "js/CallAndConstruct.h"    // JS_CallFunctionName
+#include "js/PropertyAndElement.h"  // JS_Enumerate, JS_GetElement, JS_GetProperty
+#include "mozilla/CycleCollectedJSContext.h"
+#include "mozilla/gtest/MozAssertions.h"
+#include "mozilla/Unused.h"
+#include "nsTArray.h"
+#include "nsPrintfCString.h"
+
+using namespace mozilla;
+
+// Helper methods provided to simplify writing tests and meant to be used in C++
+// Gtests.
+namespace TelemetryTestHelpers {
+
+void CheckUintScalar(const char* aName, JSContext* aCx,
+                     JS::Handle<JS::Value> aSnapshot, uint32_t expectedValue) {
+  // Validate the value of the test scalar.
+  JS::Rooted<JS::Value> value(aCx);
+  JS::Rooted<JSObject*> scalarObj(aCx, &aSnapshot.toObject());
+  ASSERT_TRUE(JS_GetProperty(aCx, scalarObj, aName, &value))
+  << "The test scalar must be reported.";
+  JS_GetProperty(aCx, scalarObj, aName, &value);
+
+  ASSERT_TRUE(value.isInt32())
+  << "The scalar value must be of the correct type.";
+  ASSERT_TRUE(value.toInt32() >= 0)
+  << "The uint scalar type must contain a value >= 0.";
+  ASSERT_EQ(static_cast<uint32_t>(value.toInt32()), expectedValue)
+      << "The scalar value must match the expected value.";
+}
+
+void CheckBoolScalar(const char* aName, JSContext* aCx,
+                     JS::Handle<JS::Value> aSnapshot, bool expectedValue) {
+  // Validate the value of the test scalar.
+  JS::Rooted<JS::Value> value(aCx);
+  JS::Rooted<JSObject*> scalarObj(aCx, &aSnapshot.toObject());
+  ASSERT_TRUE(JS_GetProperty(aCx, scalarObj, aName, &value))
+  << "The test scalar must be reported.";
+  ASSERT_TRUE(value.isBoolean())
+  << "The scalar value must be of the correct type.";
+  ASSERT_EQ(static_cast<bool>(value.toBoolean()), expectedValue)
+      << "The scalar value must match the expected value.";
+}
+
+void CheckStringScalar(const char* aName, JSContext* aCx,
+                       JS::Handle<JS::Value> aSnapshot,
+                       const char* expectedValue) {
+  // Validate the value of the test scalar.
+  JS::Rooted<JS::Value> value(aCx);
+  JS::Rooted<JSObject*> scalarObj(aCx, &aSnapshot.toObject());
+  ASSERT_TRUE(JS_GetProperty(aCx, scalarObj, aName, &value))
+  << "The test scalar must be reported.";
+  ASSERT_TRUE(value.isString())
+  << "The scalar value must be of the correct type.";
+
+  bool sameString;
+  ASSERT_TRUE(
+      JS_StringEqualsAscii(aCx, value.toString(), expectedValue, &sameString))
+  << "JS String comparison failed";
+  ASSERT_TRUE(sameString)
+  << "The scalar value must match the expected string";
+}
+
+void CheckKeyedUintScalar(const char* aName, const char* aKey, JSContext* aCx,
+                          JS::Handle<JS::Value> aSnapshot,
+                          uint32_t expectedValue) {
+  JS::Rooted<JS::Value> keyedScalar(aCx);
+  JS::Rooted<JSObject*> scalarObj(aCx, &aSnapshot.toObject());
+  // Get the aName keyed scalar object from the scalars snapshot.
+  ASSERT_TRUE(JS_GetProperty(aCx, scalarObj, aName, &keyedScalar))
+  << "The keyed scalar must be reported.";
+
+  CheckUintScalar(aKey, aCx, keyedScalar, expectedValue);
+}
+
+void CheckKeyedBoolScalar(const char* aName, const char* aKey, JSContext* aCx,
+                          JS::Handle<JS::Value> aSnapshot, bool expectedValue) {
+  JS::Rooted<JS::Value> keyedScalar(aCx);
+  JS::Rooted<JSObject*> scalarObj(aCx, &aSnapshot.toObject());
+  // Get the aName keyed scalar object from the scalars snapshot.
+  ASSERT_TRUE(JS_GetProperty(aCx, scalarObj, aName, &keyedScalar))
+  << "The keyed scalar must be reported.";
+
+  CheckBoolScalar(aKey, aCx, keyedScalar, expectedValue);
+}
+
+void CheckNumberOfProperties(const char* aName, JSContext* aCx,
+                             JS::Handle<JS::Value> aSnapshot,
+                             uint32_t expectedNumProperties) {
+  JS::Rooted<JS::Value> keyedScalar(aCx);
+  JS::Rooted<JSObject*> scalarObj(aCx, &aSnapshot.toObject());
+  // Get the aName keyed scalar object from the scalars snapshot.
+  ASSERT_TRUE(JS_GetProperty(aCx, scalarObj, aName, &keyedScalar))
+  << "The keyed scalar must be reported.";
+
+  JS::Rooted<JSObject*> keyedScalarObj(aCx, &keyedScalar.toObject());
+  JS::Rooted<JS::IdVector> ids(aCx, JS::IdVector(aCx));
+  ASSERT_TRUE(JS_Enumerate(aCx, keyedScalarObj, &ids))
+  << "We must be able to get keyed scalar members.";
+
+  ASSERT_EQ(expectedNumProperties, ids.length())
+      << "The scalar must report the expected number of properties.";
+}
+
+bool EventPresent(JSContext* aCx, const JS::RootedValue& aSnapshot,
+                  const nsACString& aCategory, const nsACString& aMethod,
+                  const nsACString& aObject) {
+  EXPECT_FALSE(aSnapshot.isNullOrUndefined())
+      << "Event snapshot must not be null/undefined.";
+  bool isArray = false;
+  EXPECT_TRUE(JS::IsArrayObject(aCx, aSnapshot, &isArray) && isArray)
+      << "The snapshot must be an array.";
+  JS::Rooted<JSObject*> arrayObj(aCx, &aSnapshot.toObject());
+  uint32_t arrayLength = 0;
+  EXPECT_TRUE(JS::GetArrayLength(aCx, arrayObj, &arrayLength))
+      << "Array must have a length.";
+  EXPECT_TRUE(arrayLength > 0) << "Array must have at least one element.";
+
+  for (uint32_t arrayIdx = 0; arrayIdx < arrayLength; ++arrayIdx) {
+    JS::Rooted<JS::Value> element(aCx);
+    EXPECT_TRUE(JS_GetElement(aCx, arrayObj, arrayIdx, &element))
+        << "Must be able to get element.";
+    EXPECT_TRUE(JS::IsArrayObject(aCx, element, &isArray) && isArray)
+        << "Element must be an array.";
+    JS::Rooted<JSObject*> eventArray(aCx, &element.toObject());
+    uint32_t eventLength;
+    EXPECT_TRUE(JS::GetArrayLength(aCx, eventArray, &eventLength))
+        << "Event array must have a length.";
+    EXPECT_TRUE(eventLength >= 4)
+        << "Event array must have at least 4 elements (timestamp, category, "
+           "method, object).";
+
+    JS::Rooted<JS::Value> str(aCx);
+    nsAutoJSString jsStr;
+    EXPECT_TRUE(JS_GetElement(aCx, eventArray, 1, &str))
+        << "Must be able to get category.";
+    EXPECT_TRUE(str.isString()) << "Category must be a string.";
+    EXPECT_TRUE(jsStr.init(aCx, str))
+        << "Category must be able to be init'd to a jsstring.";
+    if (NS_ConvertUTF16toUTF8(jsStr) != aCategory) {
+      continue;
+    }
+
+    EXPECT_TRUE(JS_GetElement(aCx, eventArray, 2, &str))
+        << "Must be able to get method.";
+    EXPECT_TRUE(str.isString()) << "Method must be a string.";
+    EXPECT_TRUE(jsStr.init(aCx, str))
+        << "Method must be able to be init'd to a jsstring.";
+    if (NS_ConvertUTF16toUTF8(jsStr) != aMethod) {
+      continue;
+    }
+
+    EXPECT_TRUE(JS_GetElement(aCx, eventArray, 3, &str))
+        << "Must be able to get object.";
+    EXPECT_TRUE(str.isString()) << "Object must be a string.";
+    EXPECT_TRUE(jsStr.init(aCx, str))
+        << "Object must be able to be init'd to a jsstring.";
+    if (NS_ConvertUTF16toUTF8(jsStr) != aObject) {
+      continue;
+    }
+
+    // We found it!
+    return true;
+  }
+
+  // We didn't find it!
+  return false;
+}
+
+nsTArray<nsString> EventValuesToArray(JSContext* aCx,
+                                      const JS::RootedValue& aSnapshot,
+                                      const nsAString& aCategory,
+                                      const nsAString& aMethod,
+                                      const nsAString& aObject) {
+  constexpr int kIndexOfCategory = 1;
+  constexpr int kIndexOfMethod = 2;
+  constexpr int kIndexOfObject = 3;
+  constexpr int kIndexOfValueString = 4;
+
+  nsTArray<nsString> valueArray;
+  if (aSnapshot.isNullOrUndefined()) {
+    return valueArray;
+  }
+
+  bool isArray = false;
+  EXPECT_TRUE(JS::IsArrayObject(aCx, aSnapshot, &isArray) && isArray)
+      << "The snapshot must be an array.";
+
+  JS::Rooted<JSObject*> arrayObj(aCx, &aSnapshot.toObject());
+
+  uint32_t arrayLength = 0;
+  EXPECT_TRUE(JS::GetArrayLength(aCx, arrayObj, &arrayLength))
+      << "Array must have a length.";
+
+  JS::Rooted<JS::Value> jsVal(aCx);
+  nsAutoJSString jsStr;
+
+  for (uint32_t arrayIdx = 0; arrayIdx < arrayLength; ++arrayIdx) {
+    JS::Rooted<JS::Value> element(aCx);
+    EXPECT_TRUE(JS_GetElement(aCx, arrayObj, arrayIdx, &element))
+        << "Must be able to get element.";
+
+    EXPECT_TRUE(JS::IsArrayObject(aCx, element, &isArray) && isArray)
+        << "Element must be an array.";
+
+    JS::Rooted<JSObject*> eventArray(aCx, &element.toObject());
+    uint32_t eventLength;
+    EXPECT_TRUE(JS::GetArrayLength(aCx, eventArray, &eventLength))
+        << "Event array must have a length.";
+    EXPECT_TRUE(eventLength >= kIndexOfValueString)
+        << "Event array must have at least 4 elements (timestamp, category, "
+           "method, object).";
+
+    EXPECT_TRUE(JS_GetElement(aCx, eventArray, kIndexOfCategory, &jsVal))
+        << "Must be able to get category.";
+    EXPECT_TRUE(jsVal.isString()) << "Category must be a string.";
+    EXPECT_TRUE(jsStr.init(aCx, jsVal))
+        << "Category must be able to be init'd to a jsstring.";
+    if (jsStr != aCategory) {
+      continue;
+    }
+
+    EXPECT_TRUE(JS_GetElement(aCx, eventArray, kIndexOfMethod, &jsVal))
+        << "Must be able to get method.";
+    EXPECT_TRUE(jsVal.isString()) << "Method must be a string.";
+    EXPECT_TRUE(jsStr.init(aCx, jsVal))
+        << "Method must be able to be init'd to a jsstring.";
+    if (jsStr != aMethod) {
+      continue;
+    }
+
+    EXPECT_TRUE(JS_GetElement(aCx, eventArray, kIndexOfObject, &jsVal))
+        << "Must be able to get object.";
+    EXPECT_TRUE(jsVal.isString()) << "Object must be a string.";
+    EXPECT_TRUE(jsStr.init(aCx, jsVal))
+        << "Object must be able to be init'd to a jsstring.";
+    if (jsStr != aObject) {
+      continue;
+    }
+
+    if (!JS_GetElement(aCx, eventArray, kIndexOfValueString, &jsVal)) {
+      continue;
+    }
+
+    nsString str;
+    EXPECT_TRUE(AssignJSString(aCx, str, jsVal.toString()))
+        << "Value must be able to be init'd to a string.";
+    Unused << valueArray.EmplaceBack(std::move(str));
+  }
+
+  return valueArray;
+}
+
+void GetEventSnapshot(JSContext* aCx, JS::MutableHandle<JS::Value> aResult,
+                      ProcessID aProcessType) {
+  nsCOMPtr<nsITelemetry> telemetry =
+      do_GetService("@mozilla.org/base/telemetry;1");
+
+  JS::Rooted<JS::Value> eventSnapshot(aCx);
+  nsresult rv;
+  rv = telemetry->SnapshotEvents(1 /* PRERELEASE_CHANNELS */, false /* clear */,
+                                 0 /* eventLimit */, aCx, 1 /* argc */,
+                                 &eventSnapshot);
+  ASSERT_EQ(rv, NS_OK) << "Snapshotting events must not fail.";
+  ASSERT_TRUE(eventSnapshot.isObject())
+  << "The snapshot must be an object.";
+
+  JS::Rooted<JS::Value> processEvents(aCx);
+  JS::Rooted<JSObject*> eventObj(aCx, &eventSnapshot.toObject());
+  Unused << JS_GetProperty(aCx, eventObj,
+                           Telemetry::Common::GetNameForProcessID(aProcessType),
+                           &processEvents);
+
+  aResult.set(processEvents);
+}
+
+void GetScalarsSnapshot(bool aKeyed, JSContext* aCx,
+                        JS::MutableHandle<JS::Value> aResult,
+                        ProcessID aProcessType) {
+  nsCOMPtr<nsITelemetry> telemetry =
+      do_GetService("@mozilla.org/base/telemetry;1");
+
+  // Get a snapshot of the scalars.
+  JS::Rooted<JS::Value> scalarsSnapshot(aCx);
+  nsresult rv;
+
+  if (aKeyed) {
+    rv = telemetry->GetSnapshotForKeyedScalars(
+        "main"_ns, false, false /* filter */, aCx, &scalarsSnapshot);
+  } else {
+    rv = telemetry->GetSnapshotForScalars("main"_ns, false, false /* filter */,
+                                          aCx, &scalarsSnapshot);
+  }
+
+  // Validate the snapshot.
+  ASSERT_EQ(rv, NS_OK) << "Creating a snapshot of the data must not fail.";
+  ASSERT_TRUE(scalarsSnapshot.isObject())
+  << "The snapshot must be an object.";
+
+  JS::Rooted<JS::Value> processScalars(aCx);
+  JS::Rooted<JSObject*> scalarObj(aCx, &scalarsSnapshot.toObject());
+  // Don't complain if no scalars for the process can be found. Just
+  // return an empty object.
+  Unused << JS_GetProperty(aCx, scalarObj,
+                           Telemetry::Common::GetNameForProcessID(aProcessType),
+                           &processScalars);
+
+  aResult.set(processScalars);
+}
+
+void GetAndClearHistogram(JSContext* cx, nsCOMPtr<nsITelemetry> mTelemetry,
+                          const nsACString& name, bool is_keyed) {
+  JS::Rooted<JS::Value> testHistogram(cx);
+  nsresult rv =
+      is_keyed ? mTelemetry->GetKeyedHistogramById(name, cx, &testHistogram)
+               : mTelemetry->GetHistogramById(name, cx, &testHistogram);
+
+  ASSERT_EQ(rv, NS_OK) << "Cannot fetch histogram";
+
+  // Clear the stored value
+  JS::Rooted<JSObject*> testHistogramObj(cx, &testHistogram.toObject());
+  JS::Rooted<JS::Value> rval(cx);
+  ASSERT_TRUE(JS_CallFunctionName(cx, testHistogramObj, "clear",
+                                  JS::HandleValueArray::empty(), &rval))
+  << "Cannot clear histogram";
+}
+
+void GetProperty(JSContext* cx, const char* name, JS::Handle<JS::Value> valueIn,
+                 JS::MutableHandle<JS::Value> valueOut) {
+  JS::Rooted<JS::Value> property(cx);
+  JS::Rooted<JSObject*> valueInObj(cx, &valueIn.toObject());
+  ASSERT_TRUE(JS_GetProperty(cx, valueInObj, name, &property))
+  << "Cannot get property '" << name << "'";
+  valueOut.set(property);
+}
+
+void GetElement(JSContext* cx, uint32_t index, JS::Handle<JS::Value> valueIn,
+                JS::MutableHandle<JS::Value> valueOut) {
+  JS::Rooted<JS::Value> element(cx);
+  JS::Rooted<JSObject*> valueInObj(cx, &valueIn.toObject());
+  ASSERT_TRUE(JS_GetElement(cx, valueInObj, index, &element))
+  << "Cannot get element at index '" << index << "'";
+  valueOut.set(element);
+}
+
+void GetSnapshots(JSContext* cx, nsCOMPtr<nsITelemetry> mTelemetry,
+                  const char* name, JS::MutableHandle<JS::Value> valueOut,
+                  bool is_keyed) {
+  JS::Rooted<JS::Value> snapshots(cx);
+  nsresult rv = is_keyed
+                    ? mTelemetry->GetSnapshotForKeyedHistograms(
+                          "main"_ns, false, false /* filter */, cx, &snapshots)
+                    : mTelemetry->GetSnapshotForHistograms(
+                          "main"_ns, false, false /* filter */, cx, &snapshots);
+
+  JS::Rooted<JS::Value> snapshot(cx);
+  GetProperty(cx, "parent", snapshots, &snapshot);
+
+  ASSERT_EQ(rv, NS_OK) << "Cannot call histogram snapshots";
+  valueOut.set(snapshot);
+}
+
+}  // namespace TelemetryTestHelpers
diff --git a/toolkit/components/telemetry/tests/gtest/TelemetryTestHelpers.h b/toolkit/components/telemetry/tests/gtest/TelemetryTestHelpers.h
new file mode 100644
index 0000000000..b2eab48c73
--- /dev/null
+++ b/toolkit/components/telemetry/tests/gtest/TelemetryTestHelpers.h
@@ -0,0 +1,68 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+
+#ifndef TelemetryTestHelpers_h_
+#define TelemetryTestHelpers_h_
+
+#include "js/TypeDecls.h"
+#include "mozilla/TelemetryProcessEnums.h"
+#include "nsITelemetry.h"
+
+using mozilla::Telemetry::ProcessID;
+
+namespace TelemetryTestHelpers {
+
+void CheckUintScalar(const char* aName, JSContext* aCx,
+                     JS::Handle<JS::Value> aSnapshot, uint32_t expectedValue);
+
+void CheckBoolScalar(const char* aName, JSContext* aCx,
+                     JS::Handle<JS::Value> aSnapshot, bool expectedValue);
+
+void CheckStringScalar(const char* aName, JSContext* aCx,
+                       JS::Handle<JS::Value> aSnapshot,
+                       const char* expectedValue);
+
+void CheckKeyedUintScalar(const char* aName, const char* aKey, JSContext* aCx,
+                          JS::Handle<JS::Value> aSnapshot,
+                          uint32_t expectedValue);
+
+void CheckKeyedBoolScalar(const char* aName, const char* aKey, JSContext* aCx,
+                          JS::Handle<JS::Value> aSnapshot, bool expectedValue);
+
+void CheckNumberOfProperties(const char* aName, JSContext* aCx,
+                             JS::Handle<JS::Value> aSnapshot,
+                             uint32_t expectedNumProperties);
+
+bool EventPresent(JSContext* aCx, const JS::RootedValue& aSnapshot,
+                  const nsACString& aCategory, const nsACString& aMethod,
+                  const nsACString& aObject);
+
+nsTArray<nsString> EventValuesToArray(JSContext* aCx,
+                                      const JS::RootedValue& aSnapshot,
+                                      const nsAString& aCategory,
+                                      const nsAString& aMethod,
+                                      const nsAString& aObject);
+
+void GetEventSnapshot(JSContext* aCx, JS::MutableHandle<JS::Value> aResult,
+                      ProcessID aProcessType = ProcessID::Parent);
+
+void GetScalarsSnapshot(bool aKeyed, JSContext* aCx,
+                        JS::MutableHandle<JS::Value> aResult,
+                        ProcessID aProcessType = ProcessID::Parent);
+
+void GetAndClearHistogram(JSContext* cx, nsCOMPtr<nsITelemetry> mTelemetry,
+                          const nsACString& name, bool is_keyed);
+
+void GetProperty(JSContext* cx, const char* name, JS::Handle<JS::Value> valueIn,
+                 JS::MutableHandle<JS::Value> valueOut);
+
+void GetElement(JSContext* cx, uint32_t index, JS::Handle<JS::Value> valueIn,
+                JS::MutableHandle<JS::Value> valueOut);
+
+void GetSnapshots(JSContext* cx, nsCOMPtr<nsITelemetry> mTelemetry,
+                  const char* name, JS::MutableHandle<JS::Value> valueOut,
+                  bool is_keyed);
+}  // namespace TelemetryTestHelpers
+
+#endif
diff --git a/toolkit/components/telemetry/tests/gtest/TestCombinedStacks.cpp b/toolkit/components/telemetry/tests/gtest/TestCombinedStacks.cpp
new file mode 100644
index 0000000000..3e21c7378c
--- /dev/null
+++ b/toolkit/components/telemetry/tests/gtest/TestCombinedStacks.cpp
@@ -0,0 +1,158 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+
+#include "TelemetryFixture.h"
+#include "TelemetryTestHelpers.h"
+#include "other/CombinedStacks.h"
+#include "other/ProcessedStack.h"
+#include "nsPrintfCString.h"
+
+using namespace mozilla::Telemetry;
+using namespace TelemetryTestHelpers;
+
+TEST_F(TelemetryTestFixture, CombinedStacks) {
+  const size_t kMaxStacksKept = 10;
+  CombinedStacks stacks(kMaxStacksKept);
+
+  size_t iterations = kMaxStacksKept * 2;
+  for (size_t i = 0; i < iterations; ++i) {
+    ProcessedStack stack;
+    ProcessedStack::Frame frame = {static_cast<uint16_t>(i)};
+    const nsAutoString& name =
+        NS_ConvertUTF8toUTF16(nsPrintfCString("test%zu", i));
+    ProcessedStack::Module module = {name};
+
+    stack.AddFrame(frame);
+    stack.AddModule(module);
+    stacks.AddStack(stack);
+  }
+
+  ASSERT_EQ(stacks.GetStackCount(), kMaxStacksKept) << "Wrong number of stacks";
+  ASSERT_EQ(stacks.GetModuleCount(), kMaxStacksKept * 2)
+      << "Wrong number of modules";
+
+  for (size_t i = 0; i < kMaxStacksKept; ++i) {
+    ProcessedStack::Frame frame = stacks.GetStack(i)[0];
+    ASSERT_EQ(frame.mOffset, kMaxStacksKept + i)
+        << "Frame is not returning expected value";
+
+    ProcessedStack::Module module = stacks.GetModule(frame.mModIndex);
+    nsPrintfCString moduleName("test%hu", frame.mModIndex);
+    ASSERT_TRUE(module.mName.Equals(NS_ConvertUTF8toUTF16(moduleName)))
+    << "Module should have expected name";
+  }
+
+  for (size_t i = 0; i < kMaxStacksKept; ++i) {
+    stacks.RemoveStack(kMaxStacksKept - i - 1);
+    ASSERT_EQ(stacks.GetStackCount(), kMaxStacksKept - i - 1)
+        << "Stack should be removed";
+  }
+}
+
+template <int N>
+ProcessedStack MakeStack(const nsLiteralString (&aModules)[N],
+                         const uintptr_t (&aOffsets)[N]) {
+  ProcessedStack stack;
+  for (int i = 0; i < N; ++i) {
+    ProcessedStack::Frame frame = {aOffsets[i]};
+    if (aModules[i].IsEmpty()) {
+      frame.mModIndex = std::numeric_limits<uint16_t>::max();
+    } else {
+      frame.mModIndex = stack.GetNumModules();
+      stack.AddModule(ProcessedStack::Module{aModules[i]});
+    }
+    stack.AddFrame(frame);
+  }
+  return stack;
+}
+
+TEST(CombinedStacks, Combine)
+{
+  const nsLiteralString moduleSet1[] = {u"mod1"_ns, u"mod2"_ns, u"base"_ns};
+  const nsLiteralString moduleSet2[] = {u"modX"_ns, u""_ns, u"modZ"_ns,
+                                        u"base"_ns};
+  // [0] 00 mod1+100
+  //     01 mod2+200
+  //     02 base+300
+  // [1] 00 mod1+1000
+  //     01 mod2+2000
+  //     02 base+3000
+  // [2] 00 modX+100
+  //     01 <no module>+200
+  //     02 modZ+300
+  //     03 base+400
+  // [3] 00 modX+1000
+  //     01 <no module>+3000
+  //     02 modZ+2000
+  //     03 base+4000
+  const ProcessedStack testStacks[] = {
+      MakeStack(moduleSet1, {100ul, 200ul, 300ul}),
+      MakeStack(moduleSet1, {1000ul, 2000ul, 3000ul}),
+      MakeStack(moduleSet2, {100ul, 200ul, 300ul, 400ul}),
+      MakeStack(moduleSet2, {1000ul, 2000ul, 3000ul, 4000ul}),
+  };
+
+  // combined1 <-- testStacks[0] + testStacks[1]
+  // combined2 <-- testStacks[2] + testStacks[3]
+  CombinedStacks combined1, combined2;
+  combined1.AddStack(testStacks[0]);
+  combined1.AddStack(testStacks[1]);
+  combined2.AddStack(testStacks[2]);
+  combined2.AddStack(testStacks[3]);
+
+  EXPECT_EQ(combined1.GetModuleCount(), mozilla::ArrayLength(moduleSet1));
+  EXPECT_EQ(combined1.GetStackCount(), 2u);
+  EXPECT_EQ(combined2.GetModuleCount(), mozilla::ArrayLength(moduleSet2) - 1);
+  EXPECT_EQ(combined2.GetStackCount(), 2u);
+
+  // combined1 <-- combined1 + combined2
+  combined1.AddStacks(combined2);
+
+  EXPECT_EQ(combined1.GetModuleCount(), 5u);  // {mod1, mod2, modX, modZ, base}
+  EXPECT_EQ(combined1.GetStackCount(), mozilla::ArrayLength(testStacks));
+
+  for (size_t i = 0; i < combined1.GetStackCount(); ++i) {
+    const auto& expectedStack = testStacks[i];
+    const auto& actualStack = combined1.GetStack(i);
+    EXPECT_EQ(actualStack.size(), expectedStack.GetStackSize());
+    if (actualStack.size() != expectedStack.GetStackSize()) {
+      continue;
+    }
+
+    for (size_t j = 0; j < actualStack.size(); ++j) {
+      const auto& expectedFrame = expectedStack.GetFrame(j);
+      const auto& actualFrame = actualStack[j];
+
+      EXPECT_EQ(actualFrame.mOffset, expectedFrame.mOffset);
+
+      if (expectedFrame.mModIndex == std::numeric_limits<uint16_t>::max()) {
+        EXPECT_EQ(actualFrame.mModIndex, std::numeric_limits<uint16_t>::max());
+      } else {
+        EXPECT_EQ(combined1.GetModule(actualFrame.mModIndex),
+                  expectedStack.GetModule(expectedFrame.mModIndex));
+      }
+    }
+  }
+
+  // Only testStacks[3] will be stored into oneStack
+  CombinedStacks oneStack(1);
+  oneStack.AddStacks(combined1);
+
+  EXPECT_EQ(oneStack.GetStackCount(), 1u);
+  EXPECT_EQ(oneStack.GetStack(0).size(), testStacks[3].GetStackSize());
+
+  for (size_t i = 0; i < oneStack.GetStack(0).size(); ++i) {
+    const auto& expectedFrame = testStacks[3].GetFrame(i);
+    const auto& actualFrame = oneStack.GetStack(0)[i];
+
+    EXPECT_EQ(actualFrame.mOffset, expectedFrame.mOffset);
+
+    if (expectedFrame.mModIndex == std::numeric_limits<uint16_t>::max()) {
+      EXPECT_EQ(actualFrame.mModIndex, std::numeric_limits<uint16_t>::max());
+    } else {
+      EXPECT_EQ(oneStack.GetModule(actualFrame.mModIndex),
+                testStacks[3].GetModule(expectedFrame.mModIndex));
+    }
+  }
+}
diff --git a/toolkit/components/telemetry/tests/gtest/TestCounters.cpp b/toolkit/components/telemetry/tests/gtest/TestCounters.cpp
new file mode 100644
index 0000000000..79b4c66bb9
--- /dev/null
+++ b/toolkit/components/telemetry/tests/gtest/TestCounters.cpp
@@ -0,0 +1,173 @@
+/* vim:set ts=2 sw=2 sts=0 et: */
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+
+#include "gtest/gtest.h"
+#include "js/Conversions.h"
+#include "mozilla/Telemetry.h"
+#include "TelemetryFixture.h"
+#include "TelemetryTestHelpers.h"
+
+using namespace mozilla;
+using namespace TelemetryTestHelpers;
+
+TEST_F(TelemetryTestFixture, AutoCounter) {
+  const uint32_t kExpectedValue = 100;
+  AutoJSContextWithGlobal cx(mCleanGlobal);
+
+  const char* telemetryTestCountName =
+      Telemetry::GetHistogramName(Telemetry::TELEMETRY_TEST_COUNT);
+
+  GetAndClearHistogram(cx.GetJSContext(), mTelemetry, "TELEMETRY_TEST_COUNT"_ns,
+                       false);
+
+  // Accumulate in the histogram
+  {
+    Telemetry::AutoCounter<Telemetry::TELEMETRY_TEST_COUNT> autoCounter;
+    autoCounter += kExpectedValue / 2;
+  }
+  // This counter should not accumulate since it does not go out of scope
+  Telemetry::AutoCounter<Telemetry::TELEMETRY_TEST_COUNT> autoCounter;
+  autoCounter += kExpectedValue;
+  // Accumulate a second time in the histogram
+  {
+    Telemetry::AutoCounter<Telemetry::TELEMETRY_TEST_COUNT> autoCounter;
+    autoCounter += kExpectedValue / 2;
+  }
+
+  // Get a snapshot for all the histograms
+  JS::Rooted<JS::Value> snapshot(cx.GetJSContext());
+  GetSnapshots(cx.GetJSContext(), mTelemetry, telemetryTestCountName, &snapshot,
+               false);
+
+  // Get the histogram from the snapshot
+  JS::Rooted<JS::Value> histogram(cx.GetJSContext());
+  GetProperty(cx.GetJSContext(), telemetryTestCountName, snapshot, &histogram);
+
+  // Get "sum" property from histogram
+  JS::Rooted<JS::Value> sum(cx.GetJSContext());
+  GetProperty(cx.GetJSContext(), "sum", histogram, &sum);
+
+  // Check that the "sum" stored in the histogram matches with |kExpectedValue|
+  uint32_t uSum = 0;
+  JS::ToUint32(cx.GetJSContext(), sum, &uSum);
+  ASSERT_EQ(uSum, kExpectedValue)
+      << "The histogram is not returning expected value";
+}
+
+TEST_F(TelemetryTestFixture, AutoCounterUnderflow) {
+  const uint32_t kExpectedValue = 0;
+  AutoJSContextWithGlobal cx(mCleanGlobal);
+
+  const char* telemetryTestCountName =
+      Telemetry::GetHistogramName(Telemetry::TELEMETRY_TEST_COUNT);
+
+  GetAndClearHistogram(cx.GetJSContext(), mTelemetry, "TELEMETRY_TEST_COUNT"_ns,
+                       false);
+
+  // Accumulate in the histogram
+  {
+    Telemetry::AutoCounter<Telemetry::TELEMETRY_TEST_COUNT> autoCounter;
+    autoCounter += -1;
+  }
+
+  // Get a snapshot for all the histograms
+  JS::Rooted<JS::Value> snapshot(cx.GetJSContext());
+  GetSnapshots(cx.GetJSContext(), mTelemetry, telemetryTestCountName, &snapshot,
+               false);
+
+  // Get the histogram from the snapshot
+  JS::Rooted<JS::Value> histogram(cx.GetJSContext());
+  GetProperty(cx.GetJSContext(), telemetryTestCountName, snapshot, &histogram);
+
+  // Get "sum" property from histogram
+  JS::Rooted<JS::Value> sum(cx.GetJSContext());
+  GetProperty(cx.GetJSContext(), "sum", histogram, &sum);
+
+  // Check that the "sum" stored in the histogram matches with |kExpectedValue|
+  uint32_t uSum = 42;
+  JS::ToUint32(cx.GetJSContext(), sum, &uSum);
+  ASSERT_EQ(uSum, kExpectedValue)
+      << "The histogram is supposed to return 0 when an underflow occurs.";
+}
+
+TEST_F(TelemetryTestFixture, RuntimeAutoCounter) {
+  const uint32_t kExpectedValue = 100;
+  AutoJSContextWithGlobal cx(mCleanGlobal);
+
+  const char* telemetryTestCountName =
+      Telemetry::GetHistogramName(Telemetry::TELEMETRY_TEST_COUNT);
+
+  GetAndClearHistogram(cx.GetJSContext(), mTelemetry, "TELEMETRY_TEST_COUNT"_ns,
+                       false);
+
+  // Accumulate in the histogram
+  {
+    Telemetry::RuntimeAutoCounter autoCounter(Telemetry::TELEMETRY_TEST_COUNT);
+    autoCounter += kExpectedValue / 2;
+  }
+  // This counter should not accumulate since it does not go out of scope
+  Telemetry::RuntimeAutoCounter autoCounter(Telemetry::TELEMETRY_TEST_COUNT);
+  autoCounter += kExpectedValue;
+  // Accumulate a second time in the histogram
+  {
+    Telemetry::RuntimeAutoCounter autoCounter(Telemetry::TELEMETRY_TEST_COUNT);
+    autoCounter += kExpectedValue / 2;
+  }
+  // Get a snapshot for all the histograms
+  JS::Rooted<JS::Value> snapshot(cx.GetJSContext());
+  GetSnapshots(cx.GetJSContext(), mTelemetry, telemetryTestCountName, &snapshot,
+               false);
+
+  // Get the histogram from the snapshot
+  JS::Rooted<JS::Value> histogram(cx.GetJSContext());
+  GetProperty(cx.GetJSContext(), telemetryTestCountName, snapshot, &histogram);
+
+  // Get "sum" property from histogram
+  JS::Rooted<JS::Value> sum(cx.GetJSContext());
+  GetProperty(cx.GetJSContext(), "sum", histogram, &sum);
+
+  // Check that the "sum" stored in the histogram matches with |kExpectedValue|
+  uint32_t uSum = 0;
+  JS::ToUint32(cx.GetJSContext(), sum, &uSum);
+  ASSERT_EQ(uSum, kExpectedValue)
+      << "The histogram is not returning expected value";
+}
+
+TEST_F(TelemetryTestFixture, RuntimeAutoCounterUnderflow) {
+  const uint32_t kExpectedValue = 0;
+  AutoJSContextWithGlobal cx(mCleanGlobal);
+
+  const char* telemetryTestCountName =
+      Telemetry::GetHistogramName(Telemetry::TELEMETRY_TEST_COUNT);
+
+  GetAndClearHistogram(cx.GetJSContext(), mTelemetry, "TELEMETRY_TEST_COUNT"_ns,
+                       false);
+
+  // Accumulate in the histogram
+  {
+    Telemetry::RuntimeAutoCounter autoCounter(Telemetry::TELEMETRY_TEST_COUNT,
+                                              kExpectedValue);
+    autoCounter += -1;
+  }
+
+  // Get a snapshot for all the histograms
+  JS::Rooted<JS::Value> snapshot(cx.GetJSContext());
+  GetSnapshots(cx.GetJSContext(), mTelemetry, telemetryTestCountName, &snapshot,
+               false);
+
+  // Get the histogram from the snapshot
+  JS::Rooted<JS::Value> histogram(cx.GetJSContext());
+  GetProperty(cx.GetJSContext(), telemetryTestCountName, snapshot, &histogram);
+
+  // Get "sum" property from histogram
+  JS::Rooted<JS::Value> sum(cx.GetJSContext());
+  GetProperty(cx.GetJSContext(), "sum", histogram, &sum);
+
+  // Check that the "sum" stored in the histogram matches with |kExpectedValue|
+  uint32_t uSum = 42;
+  JS::ToUint32(cx.GetJSContext(), sum, &uSum);
+  ASSERT_EQ(uSum, kExpectedValue)
+      << "The histogram is supposed to return 0 when an underflow occurs.";
+}
diff --git a/toolkit/components/telemetry/tests/gtest/TestEvents.cpp b/toolkit/components/telemetry/tests/gtest/TestEvents.cpp
new file mode 100644
index 0000000000..be08f234a9
--- /dev/null
+++ b/toolkit/components/telemetry/tests/gtest/TestEvents.cpp
@@ -0,0 +1,115 @@
+/* vim:set ts=2 sw=2 sts=2 et: */
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+
+#include "core/TelemetryEvent.h"
+#include "gtest/gtest.h"
+#include "js/Array.h"               // JS::GetArrayLength
+#include "js/PropertyAndElement.h"  // JS_GetElement, JS_GetProperty
+#include "mozilla/Maybe.h"
+#include "mozilla/Telemetry.h"
+#include "mozilla/Unused.h"
+#include "TelemetryFixture.h"
+#include "TelemetryTestHelpers.h"
+
+using namespace mozilla;
+using namespace TelemetryTestHelpers;
+
+// Test that we can properly record events using the C++ API.
+TEST_F(TelemetryTestFixture, RecordEventNative) {
+  AutoJSContextWithGlobal cx(mCleanGlobal);
+
+  // Make sure we don't get events from other tests.
+  Unused << mTelemetry->ClearEvents();
+
+  const nsLiteralCString category("telemetry.test");
+  const nsLiteralCString method("test1");
+  const nsLiteralCString method2("test2");
+  const nsLiteralCString object("object1");
+  const nsLiteralCString object2("object2");
+  const nsLiteralCString value("value");
+  const nsLiteralCString valueLong(
+      "this value is much too long and must be truncated to fit in the limit "
+      "which at time of writing was 80 bytes.");
+  const nsLiteralCString extraKey("key1");
+  const nsLiteralCString extraValue("extra value");
+  const nsLiteralCString extraValueLong(
+      "this extra value is much too long and must be truncated to fit in the "
+      "limit which at time of writing was 80 bytes.");
+
+  // Try recording before category's enabled.
+  Telemetry::RecordEvent(Telemetry::EventID::TelemetryTest_Test1_Object1,
+                         Nothing(), Nothing());
+
+  // Ensure "telemetry.test" is enabled
+  Telemetry::SetEventRecordingEnabled(category, true);
+
+  // Try recording after it's enabled.
+  Telemetry::RecordEvent(Telemetry::EventID::TelemetryTest_Test2_Object1,
+                         Nothing(), Nothing());
+
+  // Try recording with normal value, extra
+  CopyableTArray<EventExtraEntry> extra(
+      {EventExtraEntry{extraKey, extraValue}});
+  Telemetry::RecordEvent(Telemetry::EventID::TelemetryTest_Test1_Object2,
+                         mozilla::Some(value), mozilla::Some(extra));
+
+  // Try recording with too-long value, extra
+  CopyableTArray<EventExtraEntry> longish(
+      {EventExtraEntry{extraKey, extraValueLong}});
+  Telemetry::RecordEvent(Telemetry::EventID::TelemetryTest_Test2_Object2,
+                         mozilla::Some(valueLong), mozilla::Some(longish));
+
+  JS::Rooted<JS::Value> eventsSnapshot(cx.GetJSContext());
+  GetEventSnapshot(cx.GetJSContext(), &eventsSnapshot);
+
+  ASSERT_TRUE(!EventPresent(cx.GetJSContext(), eventsSnapshot, category, method,
+                            object))
+  << "Test event must not be present when recorded before enabled.";
+  ASSERT_TRUE(EventPresent(cx.GetJSContext(), eventsSnapshot, category, method2,
+                           object))
+  << "Test event must be present.";
+  ASSERT_TRUE(EventPresent(cx.GetJSContext(), eventsSnapshot, category, method,
+                           object2))
+  << "Test event with value and extra must be present.";
+  ASSERT_TRUE(EventPresent(cx.GetJSContext(), eventsSnapshot, category, method2,
+                           object2))
+  << "Test event with truncated value and extra must be present.";
+
+  // Ensure that the truncations happened appropriately.
+  JSContext* aCx = cx.GetJSContext();
+  JS::Rooted<JSObject*> arrayObj(aCx, &eventsSnapshot.toObject());
+  JS::Rooted<JS::Value> eventRecord(aCx);
+  ASSERT_TRUE(JS_GetElement(aCx, arrayObj, 2, &eventRecord))
+  << "Must be able to get record.";
+  JS::Rooted<JSObject*> recordArray(aCx, &eventRecord.toObject());
+  uint32_t recordLength;
+  ASSERT_TRUE(JS::GetArrayLength(aCx, recordArray, &recordLength))
+  << "Event record array must have length.";
+  ASSERT_TRUE(recordLength == 6)
+  << "Event record must have 6 elements.";
+
+  JS::Rooted<JS::Value> str(aCx);
+  nsAutoJSString jsStr;
+  // The value string is at index 4
+  ASSERT_TRUE(JS_GetElement(aCx, recordArray, 4, &str))
+  << "Must be able to get value.";
+  ASSERT_TRUE(jsStr.init(aCx, str))
+  << "Value must be able to be init'd to a jsstring.";
+  ASSERT_EQ(NS_ConvertUTF16toUTF8(jsStr).Length(), (uint32_t)80)
+      << "Value must have been truncated to 80 bytes.";
+
+  // Extra is at index 5
+  JS::Rooted<JS::Value> obj(aCx);
+  ASSERT_TRUE(JS_GetElement(aCx, recordArray, 5, &obj))
+  << "Must be able to get extra.";
+  JS::Rooted<JSObject*> extraObj(aCx, &obj.toObject());
+  JS::Rooted<JS::Value> extraVal(aCx);
+  ASSERT_TRUE(JS_GetProperty(aCx, extraObj, extraKey.get(), &extraVal))
+  << "Must be able to get the extra key's value.";
+  ASSERT_TRUE(jsStr.init(aCx, extraVal))
+  << "Extra must be able to be init'd to a jsstring.";
+  ASSERT_EQ(NS_ConvertUTF16toUTF8(jsStr).Length(), (uint32_t)80)
+      << "Extra must have been truncated to 80 bytes.";
+}
diff --git a/toolkit/components/telemetry/tests/gtest/TestHistograms.cpp b/toolkit/components/telemetry/tests/gtest/TestHistograms.cpp
new file mode 100644
index 0000000000..28b6cce751
--- /dev/null
+++ b/toolkit/components/telemetry/tests/gtest/TestHistograms.cpp
@@ -0,0 +1,891 @@
+/* vim:set ts=2 sw=2 sts=0 et: */
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+
+#include "gtest/gtest.h"
+#include "js/Conversions.h"
+#include "mozilla/Telemetry.h"
+#include "TelemetryFixture.h"
+#include "TelemetryTestHelpers.h"
+
+using namespace mozilla;
+using namespace TelemetryTestHelpers;
+
+TEST_F(TelemetryTestFixture, AccumulateCountHistogram) {
+  const uint32_t kExpectedValue = 200;
+  AutoJSContextWithGlobal cx(mCleanGlobal);
+
+  const char* telemetryTestCountName =
+      Telemetry::GetHistogramName(Telemetry::TELEMETRY_TEST_COUNT);
+  ASSERT_STREQ(telemetryTestCountName, "TELEMETRY_TEST_COUNT")
+      << "The histogram name is wrong";
+
+  GetAndClearHistogram(cx.GetJSContext(), mTelemetry, "TELEMETRY_TEST_COUNT"_ns,
+                       false);
+
+  // Accumulate in the histogram
+  Telemetry::Accumulate(Telemetry::TELEMETRY_TEST_COUNT, kExpectedValue / 2);
+  Telemetry::Accumulate("TELEMETRY_TEST_COUNT", kExpectedValue / 2);
+
+  // Get a snapshot for all the histograms
+  JS::Rooted<JS::Value> snapshot(cx.GetJSContext());
+  GetSnapshots(cx.GetJSContext(), mTelemetry, telemetryTestCountName, &snapshot,
+               false);
+
+  // Get the histogram from the snapshot
+  JS::Rooted<JS::Value> histogram(cx.GetJSContext());
+  GetProperty(cx.GetJSContext(), telemetryTestCountName, snapshot, &histogram);
+
+  // Get "sum" property from histogram
+  JS::Rooted<JS::Value> sum(cx.GetJSContext());
+  GetProperty(cx.GetJSContext(), "sum", histogram, &sum);
+
+  // Check that the "sum" stored in the histogram matches with |kExpectedValue|
+  uint32_t uSum = 0;
+  JS::ToUint32(cx.GetJSContext(), sum, &uSum);
+  ASSERT_EQ(uSum, kExpectedValue)
+      << "The histogram is not returning expected value";
+}
+
+TEST_F(TelemetryTestFixture, AccumulateKeyedCountHistogram) {
+  const uint32_t kExpectedValue = 100;
+  AutoJSContextWithGlobal cx(mCleanGlobal);
+
+  GetAndClearHistogram(cx.GetJSContext(), mTelemetry,
+                       "TELEMETRY_TEST_KEYED_COUNT"_ns, true);
+
+  // Accumulate data in the provided key within the histogram
+  Telemetry::Accumulate(Telemetry::TELEMETRY_TEST_KEYED_COUNT, "sample"_ns,
+                        kExpectedValue);
+
+  // Get a snapshot for all the histograms
+  JS::Rooted<JS::Value> snapshot(cx.GetJSContext());
+  GetSnapshots(cx.GetJSContext(), mTelemetry, "TELEMETRY_TEST_KEYED_COUNT",
+               &snapshot, true);
+
+  // Get the histogram from the snapshot
+  JS::Rooted<JS::Value> histogram(cx.GetJSContext());
+  GetProperty(cx.GetJSContext(), "TELEMETRY_TEST_KEYED_COUNT", snapshot,
+              &histogram);
+
+  // Get "sample" property from histogram
+  JS::Rooted<JS::Value> expectedKeyData(cx.GetJSContext());
+  GetProperty(cx.GetJSContext(), "sample", histogram, &expectedKeyData);
+
+  // Get "sum" property from keyed data
+  JS::Rooted<JS::Value> sum(cx.GetJSContext());
+  GetProperty(cx.GetJSContext(), "sum", expectedKeyData, &sum);
+
+  // Check that the sum stored in the histogram matches with |kExpectedValue|
+  uint32_t uSum = 0;
+  JS::ToUint32(cx.GetJSContext(), sum, &uSum);
+  ASSERT_EQ(uSum, kExpectedValue)
+      << "The histogram is not returning expected sum";
+}
+
+TEST_F(TelemetryTestFixture, TestKeyedKeysHistogram) {
+  AutoJSContextWithGlobal cx(mCleanGlobal);
+
+  JS::Rooted<JS::Value> testHistogram(cx.GetJSContext());
+  JS::Rooted<JS::Value> rval(cx.GetJSContext());
+
+  GetAndClearHistogram(cx.GetJSContext(), mTelemetry,
+                       "TELEMETRY_TEST_KEYED_KEYS"_ns, true);
+
+  // Test the accumulation on both the allowed and unallowed keys, using
+  // the API that accepts histogram IDs.
+  Telemetry::Accumulate(Telemetry::TELEMETRY_TEST_KEYED_KEYS, "not-allowed"_ns,
+                        1);
+  Telemetry::Accumulate(Telemetry::TELEMETRY_TEST_KEYED_KEYS, "testkey"_ns, 0);
+  // Do the same, using the API that accepts the histogram name as a string.
+  Telemetry::Accumulate("TELEMETRY_TEST_KEYED_KEYS", "not-allowed"_ns, 1);
+  Telemetry::Accumulate("TELEMETRY_TEST_KEYED_KEYS", "CommonKey"_ns, 1);
+
+  // Get a snapshot for all the histograms
+  JS::Rooted<JS::Value> snapshot(cx.GetJSContext());
+  GetSnapshots(cx.GetJSContext(), mTelemetry, "TELEMETRY_TEST_KEYED_KEYS",
+               &snapshot, true);
+
+  // Get the histogram from the snapshot
+  JS::Rooted<JS::Value> histogram(cx.GetJSContext());
+  GetProperty(cx.GetJSContext(), "TELEMETRY_TEST_KEYED_KEYS", snapshot,
+              &histogram);
+
+  // Get "testkey" property from histogram and check that it stores the correct
+  // data.
+  JS::Rooted<JS::Value> expectedKeyData(cx.GetJSContext());
+  GetProperty(cx.GetJSContext(), "testkey", histogram, &expectedKeyData);
+  ASSERT_TRUE(!expectedKeyData.isUndefined())
+  << "Cannot find the expected key in the histogram data";
+  JS::Rooted<JS::Value> sum(cx.GetJSContext());
+  GetProperty(cx.GetJSContext(), "sum", expectedKeyData, &sum);
+  uint32_t uSum = 0;
+  JS::ToUint32(cx.GetJSContext(), sum, &uSum);
+  ASSERT_EQ(uSum, 0U)
+      << "The histogram is not returning expected sum for 'testkey'";
+
+  // Do the same for the "CommonKey" property.
+  GetProperty(cx.GetJSContext(), "CommonKey", histogram, &expectedKeyData);
+  ASSERT_TRUE(!expectedKeyData.isUndefined())
+  << "Cannot find the expected key in the histogram data";
+  GetProperty(cx.GetJSContext(), "sum", expectedKeyData, &sum);
+  JS::ToUint32(cx.GetJSContext(), sum, &uSum);
+  ASSERT_EQ(uSum, 1U)
+      << "The histogram is not returning expected sum for 'CommonKey'";
+
+  GetProperty(cx.GetJSContext(), "not-allowed", histogram, &expectedKeyData);
+  ASSERT_TRUE(expectedKeyData.isUndefined())
+  << "Unallowed keys must not be recorded in the histogram data";
+
+  // The 'not-allowed' key accumulation for 'TELEMETRY_TESTED_KEYED_KEYS' was
+  // attemtped twice, so we expect the count of
+  // 'telemetry.accumulate_unknown_histogram_keys' to be 2
+  const uint32_t expectedAccumulateUnknownCount = 2;
+  JS::Rooted<JS::Value> scalarsSnapshot(cx.GetJSContext());
+  GetScalarsSnapshot(true, cx.GetJSContext(), &scalarsSnapshot);
+  CheckKeyedUintScalar("telemetry.accumulate_unknown_histogram_keys",
+                       "TELEMETRY_TEST_KEYED_KEYS", cx.GetJSContext(),
+                       scalarsSnapshot, expectedAccumulateUnknownCount);
+}
+
+TEST_F(TelemetryTestFixture, AccumulateCategoricalHistogram) {
+  const uint32_t kExpectedValue = 2;
+
+  AutoJSContextWithGlobal cx(mCleanGlobal);
+
+  GetAndClearHistogram(cx.GetJSContext(), mTelemetry,
+                       "TELEMETRY_TEST_CATEGORICAL"_ns, false);
+
+  // Accumulate one unit into the categorical histogram with label
+  // Telemetry::LABELS_TELEMETRY_TEST_CATEGORICAL::CommonLabel
+  Telemetry::AccumulateCategorical(
+      Telemetry::LABELS_TELEMETRY_TEST_CATEGORICAL::CommonLabel);
+
+  // Accumulate another unit into the same categorical histogram using a string
+  // label
+  Telemetry::AccumulateCategorical(Telemetry::TELEMETRY_TEST_CATEGORICAL,
+                                   "CommonLabel"_ns);
+
+  // Get a snapshot for all the histograms
+  JS::Rooted<JS::Value> snapshot(cx.GetJSContext());
+  GetSnapshots(cx.GetJSContext(), mTelemetry, "TELEMETRY_TEST_CATEGORICAL",
+               &snapshot, false);
+
+  // Get our histogram from the snapshot
+  JS::Rooted<JS::Value> histogram(cx.GetJSContext());
+  GetProperty(cx.GetJSContext(), "TELEMETRY_TEST_CATEGORICAL", snapshot,
+              &histogram);
+
+  // Get values object from histogram. Each entry in the object maps to a label
+  // in the histogram.
+  JS::Rooted<JS::Value> values(cx.GetJSContext());
+  GetProperty(cx.GetJSContext(), "values", histogram, &values);
+
+  // Get the value for the label we care about
+  JS::Rooted<JS::Value> value(cx.GetJSContext());
+  GetElement(cx.GetJSContext(),
+             static_cast<uint32_t>(
+                 Telemetry::LABELS_TELEMETRY_TEST_CATEGORICAL::CommonLabel),
+             values, &value);
+
+  // Check that the value stored in the histogram matches with |kExpectedValue|
+  uint32_t uValue = 0;
+  JS::ToUint32(cx.GetJSContext(), value, &uValue);
+  ASSERT_EQ(uValue, kExpectedValue)
+      << "The histogram is not returning expected value";
+}
+
+TEST_F(TelemetryTestFixture, AccumulateKeyedCategoricalHistogram) {
+  const uint32_t kSampleExpectedValue = 2;
+  const uint32_t kOtherSampleExpectedValue = 1;
+
+  AutoJSContextWithGlobal cx(mCleanGlobal);
+
+  GetAndClearHistogram(cx.GetJSContext(), mTelemetry,
+                       "TELEMETRY_TEST_KEYED_CATEGORICAL"_ns, true);
+
+  // Accumulate one unit into the categorical histogram with label
+  // Telemetry::LABELS_TELEMETRY_TEST_KEYED_CATEGORICAL::CommonLabel
+  Telemetry::AccumulateCategoricalKeyed(
+      "sample"_ns,
+      Telemetry::LABELS_TELEMETRY_TEST_KEYED_CATEGORICAL::CommonLabel);
+  // Accumulate another unit into the same categorical histogram
+  Telemetry::AccumulateCategoricalKeyed(
+      "sample"_ns,
+      Telemetry::LABELS_TELEMETRY_TEST_KEYED_CATEGORICAL::CommonLabel);
+  // Accumulate another unit into a different categorical histogram
+  Telemetry::AccumulateCategoricalKeyed(
+      "other-sample"_ns,
+      Telemetry::LABELS_TELEMETRY_TEST_KEYED_CATEGORICAL::CommonLabel);
+
+  // Get a snapshot for all the histograms
+  JS::Rooted<JS::Value> snapshot(cx.GetJSContext());
+  GetSnapshots(cx.GetJSContext(), mTelemetry,
+               "TELEMETRY_TEST_KEYED_CATEGORICAL", &snapshot, true);
+  // Get the histogram from the snapshot
+  JS::Rooted<JS::Value> histogram(cx.GetJSContext());
+  GetProperty(cx.GetJSContext(), "TELEMETRY_TEST_KEYED_CATEGORICAL", snapshot,
+              &histogram);
+
+  // Check that the sample histogram contains the values we expect
+  JS::Rooted<JS::Value> sample(cx.GetJSContext());
+  GetProperty(cx.GetJSContext(), "sample", histogram, &sample);
+  // Get values object from sample. Each entry in the object maps to a label in
+  // the histogram.
+  JS::Rooted<JS::Value> sampleValues(cx.GetJSContext());
+  GetProperty(cx.GetJSContext(), "values", sample, &sampleValues);
+  // Get the value for the label we care about
+  JS::Rooted<JS::Value> sampleValue(cx.GetJSContext());
+  GetElement(
+      cx.GetJSContext(),
+      static_cast<uint32_t>(
+          Telemetry::LABELS_TELEMETRY_TEST_KEYED_CATEGORICAL::CommonLabel),
+      sampleValues, &sampleValue);
+  // Check that the value stored in the histogram matches with
+  // |kSampleExpectedValue|
+  uint32_t uSampleValue = 0;
+  JS::ToUint32(cx.GetJSContext(), sampleValue, &uSampleValue);
+  ASSERT_EQ(uSampleValue, kSampleExpectedValue)
+      << "The sample histogram is not returning expected value";
+
+  // Check that the other-sample histogram contains the values we expect
+  JS::Rooted<JS::Value> otherSample(cx.GetJSContext());
+  GetProperty(cx.GetJSContext(), "other-sample", histogram, &otherSample);
+  // Get values object from the other-sample. Each entry in the object maps to a
+  // label in the histogram.
+  JS::Rooted<JS::Value> otherValues(cx.GetJSContext());
+  GetProperty(cx.GetJSContext(), "values", otherSample, &otherValues);
+  // Get the value for the label we care about
+  JS::Rooted<JS::Value> otherValue(cx.GetJSContext());
+  GetElement(
+      cx.GetJSContext(),
+      static_cast<uint32_t>(
+          Telemetry::LABELS_TELEMETRY_TEST_KEYED_CATEGORICAL::CommonLabel),
+      otherValues, &otherValue);
+  // Check that the value stored in the histogram matches with
+  // |kOtherSampleExpectedValue|
+  uint32_t uOtherValue = 0;
+  JS::ToUint32(cx.GetJSContext(), otherValue, &uOtherValue);
+  ASSERT_EQ(uOtherValue, kOtherSampleExpectedValue)
+      << "The other-sample histogram is not returning expected value";
+}
+
+TEST_F(TelemetryTestFixture, AccumulateCountHistogram_MultipleSamples) {
+  nsTArray<uint32_t> samples({4, 4, 4});
+  const uint32_t kExpectedSum = 12;
+
+  AutoJSContextWithGlobal cx(mCleanGlobal);
+
+  GetAndClearHistogram(cx.GetJSContext(), mTelemetry, "TELEMETRY_TEST_COUNT"_ns,
+                       false);
+
+  // Accumulate in histogram
+  Telemetry::Accumulate(Telemetry::TELEMETRY_TEST_COUNT, samples);
+
+  // Get a snapshot of all the histograms
+  JS::Rooted<JS::Value> snapshot(cx.GetJSContext());
+  GetSnapshots(cx.GetJSContext(), mTelemetry, "TELEMETRY_TEST_COUNT", &snapshot,
+               false);
+
+  // Get histogram from snapshot
+  JS::Rooted<JS::Value> histogram(cx.GetJSContext());
+  GetProperty(cx.GetJSContext(), "TELEMETRY_TEST_COUNT", snapshot, &histogram);
+
+  // Get "sum" from histogram
+  JS::Rooted<JS::Value> sum(cx.GetJSContext());
+  GetProperty(cx.GetJSContext(), "sum", histogram, &sum);
+
+  // Check that sum matches with aValue
+  uint32_t uSum = 0;
+  JS::ToUint32(cx.GetJSContext(), sum, &uSum);
+  ASSERT_EQ(uSum, kExpectedSum)
+      << "This histogram is not returning expected value";
+}
+
+TEST_F(TelemetryTestFixture, AccumulateLinearHistogram_MultipleSamples) {
+  nsTArray<uint32_t> samples({4, 4, 4});
+  const uint32_t kExpectedCount = 3;
+
+  AutoJSContextWithGlobal cx(mCleanGlobal);
+
+  GetAndClearHistogram(cx.GetJSContext(), mTelemetry,
+                       "TELEMETRY_TEST_LINEAR"_ns, false);
+
+  // Accumulate in the histogram
+  Telemetry::Accumulate(Telemetry::TELEMETRY_TEST_LINEAR, samples);
+
+  // Get a snapshot of all the histograms
+  JS::Rooted<JS::Value> snapshot(cx.GetJSContext());
+  GetSnapshots(cx.GetJSContext(), mTelemetry, "TELEMETRY_TEST_LINEAR",
+               &snapshot, false);
+
+  // Get histogram from snapshot
+  JS::Rooted<JS::Value> histogram(cx.GetJSContext());
+  GetProperty(cx.GetJSContext(), "TELEMETRY_TEST_LINEAR", snapshot, &histogram);
+
+  // Get "values" object from histogram
+  JS::Rooted<JS::Value> values(cx.GetJSContext());
+  GetProperty(cx.GetJSContext(), "values", histogram, &values);
+
+  // Index 0 is only for values less than 'low'. Values within range start at
+  // index 1
+  JS::Rooted<JS::Value> count(cx.GetJSContext());
+  const uint32_t index = 1;
+  GetElement(cx.GetJSContext(), index, values, &count);
+
+  // Check that this count matches with nSamples
+  uint32_t uCount = 0;
+  JS::ToUint32(cx.GetJSContext(), count, &uCount);
+  ASSERT_EQ(uCount, kExpectedCount)
+      << "The histogram did not accumulate the correct number of values";
+}
+
+TEST_F(TelemetryTestFixture, AccumulateLinearHistogram_DifferentSamples) {
+  nsTArray<uint32_t> samples(
+      {4, 8, 2147483646, uint32_t(INT_MAX) + 1, UINT32_MAX});
+
+  AutoJSContextWithGlobal cx(mCleanGlobal);
+
+  mTelemetry->ClearScalars();
+  GetAndClearHistogram(cx.GetJSContext(), mTelemetry,
+                       "TELEMETRY_TEST_LINEAR"_ns, false);
+
+  // Accumulate in histogram
+  Telemetry::Accumulate(Telemetry::TELEMETRY_TEST_LINEAR, samples);
+
+  // Get a snapshot of all histograms
+  JS::Rooted<JS::Value> snapshot(cx.GetJSContext());
+  GetSnapshots(cx.GetJSContext(), mTelemetry, "TELEMETRY_TEST_LINEAR",
+               &snapshot, false);
+
+  // Get histogram from snapshot
+  JS::Rooted<JS::Value> histogram(cx.GetJSContext());
+  GetProperty(cx.GetJSContext(), "TELEMETRY_TEST_LINEAR", snapshot, &histogram);
+
+  // Get values object from histogram
+  JS::Rooted<JS::Value> values(cx.GetJSContext());
+  GetProperty(cx.GetJSContext(), "values", histogram, &values);
+
+  // Get values in first and last buckets
+  JS::Rooted<JS::Value> countFirst(cx.GetJSContext());
+  JS::Rooted<JS::Value> countLast(cx.GetJSContext());
+  const uint32_t firstIndex = 1;
+  // Buckets are indexed by their start value
+  const uint32_t lastIndex = INT32_MAX - 1;
+  GetElement(cx.GetJSContext(), firstIndex, values, &countFirst);
+  GetElement(cx.GetJSContext(), lastIndex, values, &countLast);
+
+  // Check that the values match
+  uint32_t uCountFirst = 0;
+  uint32_t uCountLast = 0;
+  JS::ToUint32(cx.GetJSContext(), countFirst, &uCountFirst);
+  JS::ToUint32(cx.GetJSContext(), countLast, &uCountLast);
+
+  const uint32_t kExpectedCountFirst = 2;
+  // We expect 2147483646 to be in the last bucket, as well the two samples
+  // above 2^31 (prior to bug 1438335, values between INT_MAX and UINT32_MAX
+  // would end up as 0s)
+  const uint32_t kExpectedCountLast = 3;
+  ASSERT_EQ(uCountFirst, kExpectedCountFirst)
+      << "The first bucket did not accumulate the correct number of values";
+  ASSERT_EQ(uCountLast, kExpectedCountLast)
+      << "The last bucket did not accumulate the correct number of values";
+
+  // We accumulated two values that had to be clamped. We expect the count in
+  // 'telemetry.accumulate_clamped_values' to be 2 (only one storage).
+  const uint32_t expectedAccumulateClampedCount = 2;
+  JS::Rooted<JS::Value> scalarsSnapshot(cx.GetJSContext());
+  GetScalarsSnapshot(true, cx.GetJSContext(), &scalarsSnapshot);
+  CheckKeyedUintScalar("telemetry.accumulate_clamped_values",
+                       "TELEMETRY_TEST_LINEAR", cx.GetJSContext(),
+                       scalarsSnapshot, expectedAccumulateClampedCount);
+}
+
+TEST_F(TelemetryTestFixture, AccumulateKeyedCountHistogram_MultipleSamples) {
+  const nsTArray<uint32_t> samples({5, 10, 15});
+  const uint32_t kExpectedSum = 5 + 10 + 15;
+
+  AutoJSContextWithGlobal cx(mCleanGlobal);
+
+  GetAndClearHistogram(cx.GetJSContext(), mTelemetry,
+                       "TELEMETRY_TEST_KEYED_COUNT"_ns, true);
+
+  // Accumulate data in the provided key within the histogram
+  Telemetry::Accumulate(Telemetry::TELEMETRY_TEST_KEYED_COUNT, "sample"_ns,
+                        samples);
+
+  // Get a snapshot for all the histograms
+  JS::Rooted<JS::Value> snapshot(cx.GetJSContext());
+  GetSnapshots(cx.GetJSContext(), mTelemetry, "TELEMETRY_TEST_KEYED_COUNT",
+               &snapshot, true);
+
+  // Get the histogram from the snapshot
+  JS::Rooted<JS::Value> histogram(cx.GetJSContext());
+  GetProperty(cx.GetJSContext(), "TELEMETRY_TEST_KEYED_COUNT", snapshot,
+              &histogram);
+
+  // Get "sample" property from histogram
+  JS::Rooted<JS::Value> expectedKeyData(cx.GetJSContext());
+  GetProperty(cx.GetJSContext(), "sample", histogram, &expectedKeyData);
+
+  // Get "sum" property from keyed data
+  JS::Rooted<JS::Value> sum(cx.GetJSContext());
+  GetProperty(cx.GetJSContext(), "sum", expectedKeyData, &sum);
+
+  // Check that the sum stored in the histogram matches with |kExpectedSum|
+  uint32_t uSum = 0;
+  JS::ToUint32(cx.GetJSContext(), sum, &uSum);
+  ASSERT_EQ(uSum, kExpectedSum)
+      << "The histogram is not returning expected sum";
+}
+
+TEST_F(TelemetryTestFixture, TestKeyedLinearHistogram_MultipleSamples) {
+  AutoJSContextWithGlobal cx(mCleanGlobal);
+
+  mTelemetry->ClearScalars();
+  GetAndClearHistogram(cx.GetJSContext(), mTelemetry,
+                       "TELEMETRY_TEST_KEYED_LINEAR"_ns, true);
+
+  const nsTArray<uint32_t> samples({1, 5, 250000, UINT_MAX});
+  // Test the accumulation on the key 'testkey', using
+  // the API that accepts histogram IDs.
+  Telemetry::Accumulate(Telemetry::TELEMETRY_TEST_KEYED_LINEAR, "testkey"_ns,
+                        samples);
+
+  // Get a snapshot for all the histograms
+  JS::Rooted<JS::Value> snapshot(cx.GetJSContext());
+  GetSnapshots(cx.GetJSContext(), mTelemetry, "TELEMETRY_TEST_KEYED_LINEAR",
+               &snapshot, true);
+
+  // Get the histogram from the snapshot
+  JS::Rooted<JS::Value> histogram(cx.GetJSContext());
+  GetProperty(cx.GetJSContext(), "TELEMETRY_TEST_KEYED_LINEAR", snapshot,
+              &histogram);
+
+  // Get "testkey" property from histogram.
+  JS::Rooted<JS::Value> expectedKeyData(cx.GetJSContext());
+  GetProperty(cx.GetJSContext(), "testkey", histogram, &expectedKeyData);
+  ASSERT_TRUE(!expectedKeyData.isUndefined())
+  << "Cannot find the expected key in the histogram data";
+
+  // Get values object from 'testkey' histogram.
+  JS::Rooted<JS::Value> values(cx.GetJSContext());
+  GetProperty(cx.GetJSContext(), "values", expectedKeyData, &values);
+
+  // Get values in first and last buckets.
+  JS::Rooted<JS::Value> countFirst(cx.GetJSContext());
+  JS::Rooted<JS::Value> countLast(cx.GetJSContext());
+  const uint32_t firstIndex = 1;
+  // Buckets are indexed by their start value
+  const uint32_t lastIndex = 250000;
+  GetElement(cx.GetJSContext(), firstIndex, values, &countFirst);
+  GetElement(cx.GetJSContext(), lastIndex, values, &countLast);
+
+  // Check that the values match.
+  uint32_t uCountFirst = 0;
+  uint32_t uCountLast = 0;
+  JS::ToUint32(cx.GetJSContext(), countFirst, &uCountFirst);
+  JS::ToUint32(cx.GetJSContext(), countLast, &uCountLast);
+
+  const uint32_t kExpectedCountFirst = 2;
+  const uint32_t kExpectedCountLast = 2;
+  ASSERT_EQ(uCountFirst, kExpectedCountFirst)
+      << "The first bucket did not accumulate the correct number of values for "
+         "key 'testkey'";
+  ASSERT_EQ(uCountLast, kExpectedCountLast)
+      << "The last bucket did not accumulate the correct number of values for "
+         "key 'testkey'";
+
+  // We accumulated one keyed values that had to be clamped. We expect the
+  // count in 'telemetry.accumulate_clamped_values' to be 1
+  const uint32_t expectedAccumulateClampedCount = 1;
+  JS::Rooted<JS::Value> scalarsSnapshot(cx.GetJSContext());
+  GetScalarsSnapshot(true, cx.GetJSContext(), &scalarsSnapshot);
+  CheckKeyedUintScalar("telemetry.accumulate_clamped_values",
+                       "TELEMETRY_TEST_KEYED_LINEAR", cx.GetJSContext(),
+                       scalarsSnapshot, expectedAccumulateClampedCount);
+}
+
+TEST_F(TelemetryTestFixture, TestKeyedKeysHistogram_MultipleSamples) {
+  AutoJSContextWithGlobal cx(mCleanGlobal);
+  mTelemetry->ClearScalars();
+  const nsTArray<uint32_t> samples({false, false, true, 32, true});
+
+  GetAndClearHistogram(cx.GetJSContext(), mTelemetry,
+                       "TELEMETRY_TEST_KEYED_KEYS"_ns, true);
+
+  // Test the accumulation on both the allowed and unallowed keys, using
+  // the API that accepts histogram IDs.
+  Telemetry::Accumulate(Telemetry::TELEMETRY_TEST_KEYED_KEYS, "not-allowed"_ns,
+                        samples);
+  Telemetry::Accumulate(Telemetry::TELEMETRY_TEST_KEYED_KEYS, "testkey"_ns,
+                        samples);
+
+  // Get a snapshot for all the histograms
+  JS::Rooted<JS::Value> snapshot(cx.GetJSContext());
+  GetSnapshots(cx.GetJSContext(), mTelemetry, "TELEMETRY_TEST_KEYED_KEYS",
+               &snapshot, true);
+
+  // Get the histogram from the snapshot
+  JS::Rooted<JS::Value> histogram(cx.GetJSContext());
+  GetProperty(cx.GetJSContext(), "TELEMETRY_TEST_KEYED_KEYS", snapshot,
+              &histogram);
+
+  // Get "testkey" property from histogram and check that it stores the correct
+  // data.
+  JS::Rooted<JS::Value> testKeyData(cx.GetJSContext());
+  GetProperty(cx.GetJSContext(), "testkey", histogram, &testKeyData);
+  ASSERT_TRUE(!testKeyData.isUndefined())
+  << "Cannot find the key 'testkey' in the histogram data";
+
+  JS::Rooted<JS::Value> values(cx.GetJSContext());
+  GetProperty(cx.GetJSContext(), "values", testKeyData, &values);
+
+  // Get values in buckets 0,1,2
+  const uint32_t falseIndex = 0;
+  const uint32_t trueIndex = 1;
+  const uint32_t otherIndex = 2;
+
+  JS::Rooted<JS::Value> countFalse(cx.GetJSContext());
+  JS::Rooted<JS::Value> countTrue(cx.GetJSContext());
+  JS::Rooted<JS::Value> countOther(cx.GetJSContext());
+
+  GetElement(cx.GetJSContext(), falseIndex, values, &countFalse);
+  GetElement(cx.GetJSContext(), trueIndex, values, &countTrue);
+  GetElement(cx.GetJSContext(), otherIndex, values, &countOther);
+
+  uint32_t uCountFalse = 0;
+  uint32_t uCountTrue = 0;
+  uint32_t uCountOther = 0;
+  JS::ToUint32(cx.GetJSContext(), countFalse, &uCountFalse);
+  JS::ToUint32(cx.GetJSContext(), countTrue, &uCountTrue);
+  JS::ToUint32(cx.GetJSContext(), countOther, &uCountOther);
+
+  const uint32_t kExpectedCountFalse = 2;
+  const uint32_t kExpectedCountTrue = 3;
+  const uint32_t kExpectedCountOther = 0;
+
+  ASSERT_EQ(uCountFalse, kExpectedCountFalse)
+      << "The histogram did not accumulate the correct number of 'false' "
+         "booleans for key 'testkey'";
+  ASSERT_EQ(uCountTrue, kExpectedCountTrue)
+      << "The histogram did not accumulate the correct number of 'true' "
+         "booleans for key 'testkey'";
+  ASSERT_EQ(uCountOther, kExpectedCountOther)
+      << "The histogram did not accumulate the correct number of undefined "
+         "values for key 'testkey'";
+
+  // Here we check that we are not accumulating to a different (but still
+  // 'allowed') key. Get "CommonKey" property from histogram and check that it
+  // has no data. Since we accumulated no data to it, commonKeyData should be
+  // undefined.
+  JS::Rooted<JS::Value> commonKeyData(cx.GetJSContext());
+  GetProperty(cx.GetJSContext(), "CommonKey", histogram, &commonKeyData);
+  ASSERT_TRUE(commonKeyData.isUndefined())
+  << "Found data in key 'CommonKey' even though we accumulated no data to "
+     "it";
+
+  // Here we check that our function does not allow accumulation into unallowed
+  // keys. Get 'not-allowed' property from histogram and check that this also
+  // has no data. This should contain no data because this key is not allowed.
+  JS::Rooted<JS::Value> notAllowedKeyData(cx.GetJSContext());
+  GetProperty(cx.GetJSContext(), "not-allowed", histogram, &notAllowedKeyData);
+  ASSERT_TRUE(notAllowedKeyData.isUndefined())
+  << "Found data in key 'not-allowed' even though accumuling data to it is "
+     "not allowed";
+
+  // The 'not-allowed' key accumulation for 'TELEMETRY_TESTED_KEYED_KEYS' was
+  // attemtped once, so we expect the count of
+  // 'telemetry.accumulate_unknown_histogram_keys' to be 1
+  const uint32_t expectedAccumulateUnknownCount = 1;
+  JS::Rooted<JS::Value> scalarsSnapshot(cx.GetJSContext());
+  GetScalarsSnapshot(true, cx.GetJSContext(), &scalarsSnapshot);
+  CheckKeyedUintScalar("telemetry.accumulate_unknown_histogram_keys",
+                       "TELEMETRY_TEST_KEYED_KEYS", cx.GetJSContext(),
+                       scalarsSnapshot, expectedAccumulateUnknownCount);
+}
+
+TEST_F(TelemetryTestFixture,
+       AccumulateCategoricalHistogram_MultipleStringLabels) {
+  const uint32_t kExpectedValue = 2;
+  const nsTArray<nsCString> labels({"CommonLabel"_ns, "CommonLabel"_ns});
+  AutoJSContextWithGlobal cx(mCleanGlobal);
+
+  GetAndClearHistogram(cx.GetJSContext(), mTelemetry,
+                       "TELEMETRY_TEST_CATEGORICAL"_ns, false);
+
+  // Accumulate the units into a categorical histogram using a string label
+  Telemetry::AccumulateCategorical(Telemetry::TELEMETRY_TEST_CATEGORICAL,
+                                   labels);
+
+  // Get a snapshot for all the histograms
+  JS::Rooted<JS::Value> snapshot(cx.GetJSContext());
+  GetSnapshots(cx.GetJSContext(), mTelemetry, "TELEMETRY_TEST_CATEGORICAL",
+               &snapshot, false);
+
+  // Get our histogram from the snapshot
+  JS::Rooted<JS::Value> histogram(cx.GetJSContext());
+  GetProperty(cx.GetJSContext(), "TELEMETRY_TEST_CATEGORICAL", snapshot,
+              &histogram);
+
+  // Get values object from histogram. Each entry in the object maps to a label
+  // in the histogram.
+  JS::Rooted<JS::Value> values(cx.GetJSContext());
+  GetProperty(cx.GetJSContext(), "values", histogram, &values);
+
+  // Get the value for the label we care about
+  JS::Rooted<JS::Value> value(cx.GetJSContext());
+  GetElement(cx.GetJSContext(),
+             static_cast<uint32_t>(
+                 Telemetry::LABELS_TELEMETRY_TEST_CATEGORICAL::CommonLabel),
+             values, &value);
+
+  // Check that the value stored in the histogram matches with |kExpectedValue|
+  uint32_t uValue = 0;
+  JS::ToUint32(cx.GetJSContext(), value, &uValue);
+  ASSERT_EQ(uValue, kExpectedValue)
+      << "The histogram is not returning expected value";
+
+  // Now we check for no accumulation when a bad label is present in the array.
+  //
+  // The 'values' property is not initialized unless data is accumulated so
+  // keeping another test to check for this case alone is wasteful as we will
+  // have to accumulate some data anyway.
+
+  const nsTArray<nsCString> badLabelArray({"CommonLabel"_ns, "BadLabel"_ns});
+
+  // Try to accumulate the array into the histogram.
+  Telemetry::AccumulateCategorical(Telemetry::TELEMETRY_TEST_CATEGORICAL,
+                                   badLabelArray);
+
+  // Get snapshot of all the histograms
+  GetSnapshots(cx.GetJSContext(), mTelemetry, "TELEMETRY_TEST_CATEGORICAL",
+               &snapshot, false);
+
+  // Get our histogram from the snapshot
+  GetProperty(cx.GetJSContext(), "TELEMETRY_TEST_CATEGORICAL", snapshot,
+              &histogram);
+
+  // Get values array from histogram
+  GetProperty(cx.GetJSContext(), "values", histogram, &values);
+
+  // Get the value for the label we care about
+  GetElement(cx.GetJSContext(),
+             static_cast<uint32_t>(
+                 Telemetry::LABELS_TELEMETRY_TEST_CATEGORICAL::CommonLabel),
+             values, &value);
+
+  // Check that the value stored in the histogram matches with |kExpectedValue|
+  uValue = 0;
+  JS::ToUint32(cx.GetJSContext(), value, &uValue);
+  ASSERT_EQ(uValue, kExpectedValue)
+      << "The histogram accumulated data when it should not have";
+}
+
+TEST_F(TelemetryTestFixture,
+       AccumulateCategoricalHistogram_MultipleEnumValues) {
+  const uint32_t kExpectedValue = 2;
+  const nsTArray<Telemetry::LABELS_TELEMETRY_TEST_CATEGORICAL> enumLabels(
+      {Telemetry::LABELS_TELEMETRY_TEST_CATEGORICAL::CommonLabel,
+       Telemetry::LABELS_TELEMETRY_TEST_CATEGORICAL::CommonLabel});
+
+  AutoJSContextWithGlobal cx(mCleanGlobal);
+
+  GetAndClearHistogram(cx.GetJSContext(), mTelemetry,
+                       "TELEMETRY_TEST_CATEGORICAL"_ns, false);
+
+  // Accumulate the units into a categorical histogram using the enumLabels
+  // array
+  Telemetry::AccumulateCategorical<
+      Telemetry::LABELS_TELEMETRY_TEST_CATEGORICAL>(enumLabels);
+
+  // Get a snapshot for all the histograms
+  JS::Rooted<JS::Value> snapshot(cx.GetJSContext());
+  GetSnapshots(cx.GetJSContext(), mTelemetry, "TELEMETRY_TEST_CATEGORICAL",
+               &snapshot, false);
+
+  // Get our histogram from the snapshot
+  JS::Rooted<JS::Value> histogram(cx.GetJSContext());
+  GetProperty(cx.GetJSContext(), "TELEMETRY_TEST_CATEGORICAL", snapshot,
+              &histogram);
+
+  // Get values object from histogram. Each entry in the object maps to a label
+  // in the histogram.
+  JS::Rooted<JS::Value> values(cx.GetJSContext());
+  GetProperty(cx.GetJSContext(), "values", histogram, &values);
+
+  // Get the value for the label we care about
+  JS::Rooted<JS::Value> value(cx.GetJSContext());
+  GetElement(cx.GetJSContext(),
+             static_cast<uint32_t>(
+                 Telemetry::LABELS_TELEMETRY_TEST_CATEGORICAL::CommonLabel),
+             values, &value);
+
+  // Check that the value stored in the histogram matches with |kExpectedValue|
+  uint32_t uValue = 0;
+  JS::ToUint32(cx.GetJSContext(), value, &uValue);
+  ASSERT_EQ(uValue, kExpectedValue)
+      << "The histogram is not returning expected value";
+}
+
+TEST_F(TelemetryTestFixture,
+       AccumulateKeyedCategoricalHistogram_MultipleEnumValues) {
+  const uint32_t kExpectedCommonLabel = 2;
+  const uint32_t kExpectedLabel2 = 1;
+  const nsTArray<Telemetry::LABELS_TELEMETRY_TEST_KEYED_CATEGORICAL> enumLabels(
+      {Telemetry::LABELS_TELEMETRY_TEST_KEYED_CATEGORICAL::CommonLabel,
+       Telemetry::LABELS_TELEMETRY_TEST_KEYED_CATEGORICAL::CommonLabel,
+       Telemetry::LABELS_TELEMETRY_TEST_KEYED_CATEGORICAL::Label2});
+
+  AutoJSContextWithGlobal cx(mCleanGlobal);
+
+  GetAndClearHistogram(cx.GetJSContext(), mTelemetry,
+                       "TELEMETRY_TEST_KEYED_CATEGORICAL"_ns, true);
+
+  // Accumulate the array into the categorical keyed histogram
+  Telemetry::AccumulateCategoricalKeyed("sampleKey"_ns, enumLabels);
+
+  // Get a snapshot for all the histograms
+  JS::Rooted<JS::Value> snapshot(cx.GetJSContext());
+  GetSnapshots(cx.GetJSContext(), mTelemetry,
+               "TELEMETRY_TEST_KEYED_CATEGORICAL", &snapshot, true);
+
+  // Get the histogram from the snapshot
+  JS::Rooted<JS::Value> histogram(cx.GetJSContext());
+  GetProperty(cx.GetJSContext(), "TELEMETRY_TEST_KEYED_CATEGORICAL", snapshot,
+              &histogram);
+
+  // Check that the sampleKey histogram contains correct number of CommonLabel
+  // samples
+  JS::Rooted<JS::Value> sample(cx.GetJSContext());
+  GetProperty(cx.GetJSContext(), "sampleKey", histogram, &sample);
+
+  // Get values object from the sample. Each entry in the object maps to a label
+  // in the histogram.
+  JS::Rooted<JS::Value> sampleKeyValues(cx.GetJSContext());
+  GetProperty(cx.GetJSContext(), "values", sample, &sampleKeyValues);
+
+  // Get the count of CommonLabel
+  JS::Rooted<JS::Value> commonLabelValue(cx.GetJSContext());
+  GetElement(
+      cx.GetJSContext(),
+      static_cast<uint32_t>(
+          Telemetry::LABELS_TELEMETRY_TEST_KEYED_CATEGORICAL::CommonLabel),
+      sampleKeyValues, &commonLabelValue);
+
+  // Check that the value stored in the histogram matches with
+  // |kExpectedCommonLabel|
+  uint32_t uCommonLabelValue = 0;
+  JS::ToUint32(cx.GetJSContext(), commonLabelValue, &uCommonLabelValue);
+  ASSERT_EQ(uCommonLabelValue, kExpectedCommonLabel)
+      << "The sampleKey histogram did not accumulate the correct number of "
+         "CommonLabel samples";
+
+  // Check that the sampleKey histogram contains the correct number of Label2
+  // values Get the count of Label2
+  JS::Rooted<JS::Value> label2Value(cx.GetJSContext());
+  GetElement(cx.GetJSContext(),
+             static_cast<uint32_t>(
+                 Telemetry::LABELS_TELEMETRY_TEST_KEYED_CATEGORICAL::Label2),
+             sampleKeyValues, &label2Value);
+
+  // Check that the value stored in the histogram matches with |kExpectedLabel2|
+  uint32_t uLabel2Value = 0;
+  JS::ToUint32(cx.GetJSContext(), label2Value, &uLabel2Value);
+  ASSERT_EQ(uLabel2Value, kExpectedLabel2)
+      << "The sampleKey histogram did not accumulate the correct number of "
+         "Label2 samples";
+}
+
+TEST_F(TelemetryTestFixture, AccumulateTimeDelta) {
+  const uint32_t kExpectedValue = 100;
+  const TimeStamp start = TimeStamp::Now();
+  const TimeDuration delta = TimeDuration::FromMilliseconds(50);
+
+  AutoJSContextWithGlobal cx(mCleanGlobal);
+
+  GetAndClearHistogram(cx.GetJSContext(), mTelemetry, "TELEMETRY_TEST_COUNT"_ns,
+                       false);
+
+  // Accumulate in the histogram
+  Telemetry::AccumulateTimeDelta(Telemetry::TELEMETRY_TEST_COUNT, start - delta,
+                                 start);
+
+  Telemetry::AccumulateTimeDelta(Telemetry::TELEMETRY_TEST_COUNT, start - delta,
+                                 start);
+
+  Telemetry::AccumulateTimeDelta(Telemetry::TELEMETRY_TEST_COUNT, start, start);
+
+  // end > start timestamp gives zero contribution
+  Telemetry::AccumulateTimeDelta(Telemetry::TELEMETRY_TEST_COUNT, start + delta,
+                                 start);
+
+  // Get a snapshot for all the histograms
+  JS::Rooted<JS::Value> snapshot(cx.GetJSContext());
+  GetSnapshots(cx.GetJSContext(), mTelemetry, "TELEMETRY_TEST_COUNT", &snapshot,
+               false);
+
+  // Get the histogram from the snapshot
+  JS::Rooted<JS::Value> histogram(cx.GetJSContext());
+  GetProperty(cx.GetJSContext(), "TELEMETRY_TEST_COUNT", snapshot, &histogram);
+
+  // Get "sum" property from histogram
+  JS::Rooted<JS::Value> sum(cx.GetJSContext());
+  GetProperty(cx.GetJSContext(), "sum", histogram, &sum);
+
+  // Check that the "sum" stored in the histogram matches with |kExpectedValue|
+  uint32_t uSum = 0;
+  JS::ToUint32(cx.GetJSContext(), sum, &uSum);
+  ASSERT_EQ(uSum, kExpectedValue)
+      << "The histogram is not returning expected value";
+}
+
+TEST_F(TelemetryTestFixture, AccumulateKeyedTimeDelta) {
+  const uint32_t kExpectedValue = 100;
+  const TimeStamp start = TimeStamp::Now();
+  const TimeDuration delta = TimeDuration::FromMilliseconds(50);
+
+  AutoJSContextWithGlobal cx(mCleanGlobal);
+
+  GetAndClearHistogram(cx.GetJSContext(), mTelemetry,
+                       "TELEMETRY_TEST_KEYED_COUNT"_ns, true);
+
+  // Accumulate time delta in the provided key within the histogram
+  Telemetry::AccumulateTimeDelta(Telemetry::TELEMETRY_TEST_KEYED_COUNT,
+                                 "sample"_ns, start - delta, start);
+
+  Telemetry::AccumulateTimeDelta(Telemetry::TELEMETRY_TEST_KEYED_COUNT,
+                                 "sample"_ns, start - delta, start);
+
+  // end > start timestamp gives zero contribution
+  Telemetry::AccumulateTimeDelta(Telemetry::TELEMETRY_TEST_KEYED_COUNT,
+                                 "sample"_ns, start + delta, start);
+
+  Telemetry::AccumulateTimeDelta(Telemetry::TELEMETRY_TEST_KEYED_COUNT,
+                                 "sample"_ns, start, start);
+
+  // Get a snapshot for all the histograms
+  JS::Rooted<JS::Value> snapshot(cx.GetJSContext());
+  GetSnapshots(cx.GetJSContext(), mTelemetry, "TELEMETRY_TEST_KEYED_COUNT",
+               &snapshot, true);
+
+  // Get the histogram from the snapshot
+  JS::Rooted<JS::Value> histogram(cx.GetJSContext());
+  GetProperty(cx.GetJSContext(), "TELEMETRY_TEST_KEYED_COUNT", snapshot,
+              &histogram);
+
+  // Get "sample" property from histogram
+  JS::Rooted<JS::Value> expectedKeyData(cx.GetJSContext());
+  GetProperty(cx.GetJSContext(), "sample", histogram, &expectedKeyData);
+
+  // Get "sum" property from keyed data
+  JS::Rooted<JS::Value> sum(cx.GetJSContext());
+  GetProperty(cx.GetJSContext(), "sum", expectedKeyData, &sum);
+
+  // Check that the sum stored in the histogram matches with |kExpectedValue|
+  uint32_t uSum = 0;
+  JS::ToUint32(cx.GetJSContext(), sum, &uSum);
+  ASSERT_EQ(uSum, kExpectedValue)
+      << "The histogram is not returning expected sum";
+}
diff --git a/toolkit/components/telemetry/tests/gtest/TestScalars.cpp b/toolkit/components/telemetry/tests/gtest/TestScalars.cpp
new file mode 100644
index 0000000000..4a95ebecd0
--- /dev/null
+++ b/toolkit/components/telemetry/tests/gtest/TestScalars.cpp
@@ -0,0 +1,591 @@
+/* vim:set ts=2 sw=2 sts=2 et: */
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+
+#include "core/TelemetryScalar.h"
+#include "gtest/gtest.h"
+#include "js/Conversions.h"
+#include "js/PropertyAndElement.h"  // JS_GetProperty, JS_HasProperty
+#include "mozilla/Telemetry.h"
+#include "mozilla/TelemetryProcessEnums.h"
+#include "mozilla/Unused.h"
+#include "nsJSUtils.h"  // nsAutoJSString
+#include "nsThreadUtils.h"
+#include "TelemetryFixture.h"
+#include "TelemetryTestHelpers.h"
+
+using namespace mozilla;
+using namespace TelemetryTestHelpers;
+using mozilla::Telemetry::ProcessID;
+
+#define EXPECTED_STRING "Nice, expected and creative string."
+
+// Test that we can properly write unsigned scalars using the C++ API.
+TEST_F(TelemetryTestFixture, ScalarUnsigned) {
+  AutoJSContextWithGlobal cx(mCleanGlobal);
+
+  // Make sure we don't get scalars from other tests.
+  Unused << mTelemetry->ClearScalars();
+
+  // Set the test scalar to a known value.
+  const uint32_t kInitialValue = 1172015;
+  const uint32_t kExpectedUint = 1172017;
+  Telemetry::ScalarSet(Telemetry::ScalarID::TELEMETRY_TEST_UNSIGNED_INT_KIND,
+                       kInitialValue);
+  Telemetry::ScalarAdd(Telemetry::ScalarID::TELEMETRY_TEST_UNSIGNED_INT_KIND,
+                       kExpectedUint - kInitialValue);
+
+  // Check the recorded value.
+  JS::Rooted<JS::Value> scalarsSnapshot(cx.GetJSContext());
+  GetScalarsSnapshot(false, cx.GetJSContext(), &scalarsSnapshot);
+  CheckUintScalar("telemetry.test.unsigned_int_kind", cx.GetJSContext(),
+                  scalarsSnapshot, kExpectedUint);
+
+  // Try to use SetMaximum.
+  const uint32_t kExpectedUintMaximum = kExpectedUint * 2;
+  Telemetry::ScalarSetMaximum(
+      Telemetry::ScalarID::TELEMETRY_TEST_UNSIGNED_INT_KIND,
+      kExpectedUintMaximum);
+
+// Make sure that calls of the unsupported type don't corrupt the stored value.
+// Don't run this part in debug builds as that intentionally asserts.
+#ifndef DEBUG
+  Telemetry::ScalarSet(Telemetry::ScalarID::TELEMETRY_TEST_UNSIGNED_INT_KIND,
+                       false);
+  Telemetry::ScalarSet(Telemetry::ScalarID::TELEMETRY_TEST_UNSIGNED_INT_KIND,
+                       u"test"_ns);
+#endif
+
+  // Check the recorded value.
+  GetScalarsSnapshot(false, cx.GetJSContext(), &scalarsSnapshot);
+  CheckUintScalar("telemetry.test.unsigned_int_kind", cx.GetJSContext(),
+                  scalarsSnapshot, kExpectedUintMaximum);
+}
+
+// Test that the AutoScalarTimer records a proper uint32_t value to a
+// scalar once it goes out of scope.
+TEST_F(TelemetryTestFixture, AutoScalarTimer) {
+  AutoJSContextWithGlobal cx(mCleanGlobal);
+
+  // Make sure we don't get scalars from other tests.
+  Unused << mTelemetry->ClearScalars();
+  {
+    Telemetry::AutoScalarTimer<
+        Telemetry::ScalarID::TELEMETRY_TEST_UNSIGNED_INT_KIND>
+        timer;
+  }
+
+  const char* kScalarName = "telemetry.test.unsigned_int_kind";
+
+  // Check that there's a recorded value that is greater than 0. Since
+  // this is a timer, we'll not check the non-deterministic value - just
+  // that it exists.
+  JS::Rooted<JS::Value> scalarsSnapshot(cx.GetJSContext());
+  GetScalarsSnapshot(false, cx.GetJSContext(), &scalarsSnapshot);
+
+  // Validate the value of the test scalar.
+  JS::Rooted<JS::Value> value(cx.GetJSContext());
+  JS::Rooted<JSObject*> scalarObj(cx.GetJSContext(),
+                                  &scalarsSnapshot.toObject());
+  ASSERT_TRUE(JS_GetProperty(cx.GetJSContext(), scalarObj, kScalarName, &value))
+  << "The test scalar must be reported.";
+
+  JS_GetProperty(cx.GetJSContext(), scalarObj, kScalarName, &value);
+  ASSERT_TRUE(value.isInt32())
+  << "The scalar value must be of the correct type.";
+  ASSERT_TRUE(value.toInt32() >= 0)
+  << "The uint scalar type must contain a value >= 0.";
+}
+
+// Test that we can properly write boolean scalars using the C++ API.
+TEST_F(TelemetryTestFixture, ScalarBoolean) {
+  AutoJSContextWithGlobal cx(mCleanGlobal);
+
+  Unused << mTelemetry->ClearScalars();
+
+  // Set the test scalar to a known value.
+  Telemetry::ScalarSet(Telemetry::ScalarID::TELEMETRY_TEST_BOOLEAN_KIND, true);
+
+// Make sure that calls of the unsupported type don't corrupt the stored value.
+// Don't run this part in debug builds as that intentionally asserts.
+#ifndef DEBUG
+  Telemetry::ScalarSet(Telemetry::ScalarID::TELEMETRY_TEST_BOOLEAN_KIND,
+                       static_cast<uint32_t>(12));
+  Telemetry::ScalarSetMaximum(Telemetry::ScalarID::TELEMETRY_TEST_BOOLEAN_KIND,
+                              20);
+  Telemetry::ScalarAdd(Telemetry::ScalarID::TELEMETRY_TEST_BOOLEAN_KIND, 2);
+  Telemetry::ScalarSet(Telemetry::ScalarID::TELEMETRY_TEST_BOOLEAN_KIND,
+                       u"test"_ns);
+#endif
+
+  // Check the recorded value.
+  JS::Rooted<JS::Value> scalarsSnapshot(cx.GetJSContext());
+  GetScalarsSnapshot(false, cx.GetJSContext(), &scalarsSnapshot);
+  CheckBoolScalar("telemetry.test.boolean_kind", cx.GetJSContext(),
+                  scalarsSnapshot, true);
+}
+
+// Test that we can properly write string scalars using the C++ API.
+TEST_F(TelemetryTestFixture, ScalarString) {
+  AutoJSContextWithGlobal cx(mCleanGlobal);
+
+  Unused << mTelemetry->ClearScalars();
+
+  // Set the test scalar to a known value.
+  Telemetry::ScalarSet(Telemetry::ScalarID::TELEMETRY_TEST_STRING_KIND,
+                       NS_LITERAL_STRING_FROM_CSTRING(EXPECTED_STRING));
+
+// Make sure that calls of the unsupported type don't corrupt the stored value.
+// Don't run this part in debug builds as that intentionally asserts.
+#ifndef DEBUG
+  Telemetry::ScalarSet(Telemetry::ScalarID::TELEMETRY_TEST_STRING_KIND,
+                       static_cast<uint32_t>(12));
+  Telemetry::ScalarSetMaximum(Telemetry::ScalarID::TELEMETRY_TEST_STRING_KIND,
+                              20);
+  Telemetry::ScalarAdd(Telemetry::ScalarID::TELEMETRY_TEST_STRING_KIND, 2);
+  Telemetry::ScalarSet(Telemetry::ScalarID::TELEMETRY_TEST_STRING_KIND, true);
+#endif
+
+  // Check the recorded value.
+  JS::Rooted<JS::Value> scalarsSnapshot(cx.GetJSContext());
+  GetScalarsSnapshot(false, cx.GetJSContext(), &scalarsSnapshot);
+  CheckStringScalar("telemetry.test.string_kind", cx.GetJSContext(),
+                    scalarsSnapshot, EXPECTED_STRING);
+}
+
+// Test that we can properly write keyed unsigned scalars using the C++ API.
+TEST_F(TelemetryTestFixture, KeyedScalarUnsigned) {
+  AutoJSContextWithGlobal cx(mCleanGlobal);
+
+  Unused << mTelemetry->ClearScalars();
+
+  // Set the test scalar to a known value.
+  const char* kScalarName = "telemetry.test.keyed_unsigned_int";
+  const uint32_t kKey1Value = 1172015;
+  const uint32_t kKey2Value = 1172017;
+  Telemetry::ScalarSet(Telemetry::ScalarID::TELEMETRY_TEST_KEYED_UNSIGNED_INT,
+                       u"key1"_ns, kKey1Value);
+  Telemetry::ScalarSet(Telemetry::ScalarID::TELEMETRY_TEST_KEYED_UNSIGNED_INT,
+                       u"key2"_ns, kKey1Value);
+  Telemetry::ScalarAdd(Telemetry::ScalarID::TELEMETRY_TEST_KEYED_UNSIGNED_INT,
+                       u"key2"_ns, 2);
+
+// Make sure that calls of the unsupported type don't corrupt the stored value.
+// Don't run this part in debug builds as that intentionally asserts.
+#ifndef DEBUG
+  Telemetry::ScalarSet(Telemetry::ScalarID::TELEMETRY_TEST_KEYED_UNSIGNED_INT,
+                       u"key1"_ns, false);
+  Telemetry::ScalarSet(Telemetry::ScalarID::TELEMETRY_TEST_KEYED_UNSIGNED_INT,
+                       u"test"_ns);
+#endif
+
+  // Check the recorded value.
+  JS::Rooted<JS::Value> scalarsSnapshot(cx.GetJSContext());
+  GetScalarsSnapshot(true, cx.GetJSContext(), &scalarsSnapshot);
+
+  // Check the keyed scalar we're interested in.
+  CheckKeyedUintScalar(kScalarName, "key1", cx.GetJSContext(), scalarsSnapshot,
+                       kKey1Value);
+  CheckKeyedUintScalar(kScalarName, "key2", cx.GetJSContext(), scalarsSnapshot,
+                       kKey2Value);
+  CheckNumberOfProperties(kScalarName, cx.GetJSContext(), scalarsSnapshot, 2);
+
+  // Try to use SetMaximum.
+  const uint32_t kExpectedUintMaximum = kKey1Value * 2;
+  Telemetry::ScalarSetMaximum(
+      Telemetry::ScalarID::TELEMETRY_TEST_KEYED_UNSIGNED_INT, u"key1"_ns,
+      kExpectedUintMaximum);
+
+  GetScalarsSnapshot(true, cx.GetJSContext(), &scalarsSnapshot);
+  // The first key should be different and te second is expected to be the same.
+  CheckKeyedUintScalar(kScalarName, "key1", cx.GetJSContext(), scalarsSnapshot,
+                       kExpectedUintMaximum);
+  CheckKeyedUintScalar(kScalarName, "key2", cx.GetJSContext(), scalarsSnapshot,
+                       kKey2Value);
+  CheckNumberOfProperties(kScalarName, cx.GetJSContext(), scalarsSnapshot, 2);
+}
+
+TEST_F(TelemetryTestFixture, KeyedScalarBoolean) {
+  AutoJSContextWithGlobal cx(mCleanGlobal);
+
+  Unused << mTelemetry->ClearScalars();
+
+  // Set the test scalar to a known value.
+  Telemetry::ScalarSet(Telemetry::ScalarID::TELEMETRY_TEST_KEYED_BOOLEAN_KIND,
+                       u"key1"_ns, false);
+  Telemetry::ScalarSet(Telemetry::ScalarID::TELEMETRY_TEST_KEYED_BOOLEAN_KIND,
+                       u"key2"_ns, true);
+
+// Make sure that calls of the unsupported type don't corrupt the stored value.
+// Don't run this part in debug builds as that intentionally asserts.
+#ifndef DEBUG
+  Telemetry::ScalarSet(Telemetry::ScalarID::TELEMETRY_TEST_KEYED_BOOLEAN_KIND,
+                       u"key1"_ns, static_cast<uint32_t>(12));
+  Telemetry::ScalarSetMaximum(
+      Telemetry::ScalarID::TELEMETRY_TEST_KEYED_BOOLEAN_KIND, u"key1"_ns, 20);
+  Telemetry::ScalarAdd(Telemetry::ScalarID::TELEMETRY_TEST_KEYED_BOOLEAN_KIND,
+                       u"key1"_ns, 2);
+#endif
+
+  // Check the recorded value.
+  JS::Rooted<JS::Value> scalarsSnapshot(cx.GetJSContext());
+  GetScalarsSnapshot(true, cx.GetJSContext(), &scalarsSnapshot);
+
+  // Make sure that the keys contain the expected values.
+  const char* kScalarName = "telemetry.test.keyed_boolean_kind";
+  CheckKeyedBoolScalar(kScalarName, "key1", cx.GetJSContext(), scalarsSnapshot,
+                       false);
+  CheckKeyedBoolScalar(kScalarName, "key2", cx.GetJSContext(), scalarsSnapshot,
+                       true);
+  CheckNumberOfProperties(kScalarName, cx.GetJSContext(), scalarsSnapshot, 2);
+}
+
+TEST_F(TelemetryTestFixture, NonMainThreadAdd) {
+  AutoJSContextWithGlobal cx(mCleanGlobal);
+
+  Unused << mTelemetry->ClearScalars();
+
+  // Define the function that will be called on the testing thread.
+  nsCOMPtr<nsIRunnable> runnable = NS_NewRunnableFunction(
+      "TelemetryTestFixture_NonMainThreadAdd_Test::TestBody", []() -> void {
+        Telemetry::ScalarAdd(
+            Telemetry::ScalarID::TELEMETRY_TEST_UNSIGNED_INT_KIND, 37);
+      });
+
+  // Spawn the testing thread and run the function.
+  nsCOMPtr<nsIThread> testingThread;
+  nsresult rv =
+      NS_NewNamedThread("Test thread", getter_AddRefs(testingThread), runnable);
+  ASSERT_EQ(rv, NS_OK);
+
+  // Shutdown the thread. This also waits for the runnable to complete.
+  testingThread->Shutdown();
+
+  // Check the recorded value.
+  JS::Rooted<JS::Value> scalarsSnapshot(cx.GetJSContext());
+  GetScalarsSnapshot(false, cx.GetJSContext(), &scalarsSnapshot);
+  CheckUintScalar("telemetry.test.unsigned_int_kind", cx.GetJSContext(),
+                  scalarsSnapshot, 37);
+}
+
+TEST_F(TelemetryTestFixture, ScalarUnknownID) {
+  AutoJSContextWithGlobal cx(mCleanGlobal);
+
+  // Make sure we don't get scalars from other tests.
+  Unused << mTelemetry->ClearScalars();
+
+// Don't run this part in debug builds as that intentionally asserts.
+#ifndef DEBUG
+  const uint32_t kTestFakeIds[] = {
+      static_cast<uint32_t>(Telemetry::ScalarID::ScalarCount),
+      static_cast<uint32_t>(Telemetry::ScalarID::ScalarCount) + 378537,
+      std::numeric_limits<uint32_t>::max()};
+
+  for (auto id : kTestFakeIds) {
+    Telemetry::ScalarID scalarId = static_cast<Telemetry::ScalarID>(id);
+    Telemetry::ScalarSet(scalarId, static_cast<uint32_t>(1));
+    Telemetry::ScalarSet(scalarId, true);
+    Telemetry::ScalarSet(scalarId, u"test"_ns);
+    Telemetry::ScalarAdd(scalarId, 1);
+    Telemetry::ScalarSetMaximum(scalarId, 1);
+
+    // Make sure that nothing was recorded in the plain scalars.
+    JS::Rooted<JS::Value> scalarsSnapshot(cx.GetJSContext());
+    GetScalarsSnapshot(false, cx.GetJSContext(), &scalarsSnapshot);
+    ASSERT_TRUE(scalarsSnapshot.isUndefined())
+    << "No scalar must be recorded";
+
+    // Same for the keyed scalars.
+    Telemetry::ScalarSet(scalarId, u"key1"_ns, static_cast<uint32_t>(1));
+    Telemetry::ScalarSet(scalarId, u"key1"_ns, true);
+    Telemetry::ScalarAdd(scalarId, u"key1"_ns, 1);
+    Telemetry::ScalarSetMaximum(scalarId, u"key1"_ns, 1);
+
+    // Make sure that nothing was recorded in the keyed scalars.
+    JS::Rooted<JS::Value> keyedSnapshot(cx.GetJSContext());
+    GetScalarsSnapshot(true, cx.GetJSContext(), &keyedSnapshot);
+    ASSERT_TRUE(keyedSnapshot.isUndefined())
+    << "No keyed scalar must be recorded";
+  }
+#endif
+}
+
+TEST_F(TelemetryTestFixture, ScalarEventSummary) {
+  AutoJSContextWithGlobal cx(mCleanGlobal);
+
+  // Make sure we don't get scalars from other tests.
+  Unused << mTelemetry->ClearScalars();
+
+  const char* kScalarName = "telemetry.event_counts";
+
+  const char* kLongestEvent =
+      "oohwowlookthiscategoryissolong#thismethodislongtooo#"
+      "thisobjectisnoslouch";
+  TelemetryScalar::SummarizeEvent(nsCString(kLongestEvent), ProcessID::Parent,
+                                  false /* aDynamic */);
+
+  // Check the recorded value.
+  JS::Rooted<JS::Value> scalarsSnapshot(cx.GetJSContext());
+  GetScalarsSnapshot(true, cx.GetJSContext(), &scalarsSnapshot);
+
+  CheckKeyedUintScalar(kScalarName, kLongestEvent, cx.GetJSContext(),
+                       scalarsSnapshot, 1);
+
+// Don't run this part in debug builds as that intentionally asserts.
+#ifndef DEBUG
+  const char* kTooLongEvent =
+      "oohwowlookthiscategoryissolong#thismethodislongtooo#"
+      "thisobjectisnoslouch2";
+  TelemetryScalar::SummarizeEvent(nsCString(kTooLongEvent), ProcessID::Parent,
+                                  false /* aDynamic */);
+
+  GetScalarsSnapshot(true, cx.GetJSContext(), &scalarsSnapshot);
+  CheckNumberOfProperties(kScalarName, cx.GetJSContext(), scalarsSnapshot, 1);
+#endif  // #ifndef DEBUG
+
+  // Test we can fill the next 499 keys up to our 500 maximum
+  for (int i = 1; i < 500; i++) {
+    std::ostringstream eventName;
+    eventName << "category#method#object" << i;
+    TelemetryScalar::SummarizeEvent(nsCString(eventName.str().c_str()),
+                                    ProcessID::Parent, false /* aDynamic */);
+  }
+
+  GetScalarsSnapshot(true, cx.GetJSContext(), &scalarsSnapshot);
+  CheckNumberOfProperties(kScalarName, cx.GetJSContext(), scalarsSnapshot, 500);
+
+// Don't run this part in debug builds as that intentionally asserts.
+#ifndef DEBUG
+  TelemetryScalar::SummarizeEvent(nsCString("whoops#too#many"),
+                                  ProcessID::Parent, false /* aDynamic */);
+
+  GetScalarsSnapshot(true, cx.GetJSContext(), &scalarsSnapshot);
+  CheckNumberOfProperties(kScalarName, cx.GetJSContext(), scalarsSnapshot, 500);
+#endif  // #ifndef DEBUG
+}
+
+TEST_F(TelemetryTestFixture, ScalarEventSummary_Dynamic) {
+  AutoJSContextWithGlobal cx(mCleanGlobal);
+
+  // Make sure we don't get scalars from other tests.
+  Unused << mTelemetry->ClearScalars();
+
+  const char* kScalarName = "telemetry.dynamic_event_counts";
+  const char* kLongestEvent =
+      "oohwowlookthiscategoryissolong#thismethodislongtooo#"
+      "thisobjectisnoslouch";
+  TelemetryScalar::SummarizeEvent(nsCString(kLongestEvent), ProcessID::Parent,
+                                  true /* aDynamic */);
+  TelemetryScalar::SummarizeEvent(nsCString(kLongestEvent), ProcessID::Content,
+                                  true /* aDynamic */);
+
+  // Check the recorded value.
+  JS::Rooted<JS::Value> scalarsSnapshot(cx.GetJSContext());
+  GetScalarsSnapshot(true, cx.GetJSContext(), &scalarsSnapshot,
+                     ProcessID::Dynamic);
+
+  // Recording in parent or content doesn't matter for dynamic scalars
+  // which all end up in the same place.
+  CheckKeyedUintScalar(kScalarName, kLongestEvent, cx.GetJSContext(),
+                       scalarsSnapshot, 2);
+}
+
+TEST_F(TelemetryTestFixture, WrongScalarOperator) {
+  AutoJSContextWithGlobal cx(mCleanGlobal);
+
+  // Make sure we don't get scalars from other tests.
+  Unused << mTelemetry->ClearScalars();
+
+  const uint32_t expectedValue = 1172015;
+
+  Telemetry::ScalarSet(Telemetry::ScalarID::TELEMETRY_TEST_UNSIGNED_INT_KIND,
+                       expectedValue);
+  Telemetry::ScalarSet(Telemetry::ScalarID::TELEMETRY_TEST_STRING_KIND,
+                       NS_LITERAL_STRING_FROM_CSTRING(EXPECTED_STRING));
+  Telemetry::ScalarSet(Telemetry::ScalarID::TELEMETRY_TEST_BOOLEAN_KIND, true);
+
+  TelemetryScalar::DeserializationStarted();
+
+  Telemetry::ScalarAdd(Telemetry::ScalarID::TELEMETRY_TEST_STRING_KIND, 1447);
+  Telemetry::ScalarAdd(Telemetry::ScalarID::TELEMETRY_TEST_BOOLEAN_KIND, 1447);
+  Telemetry::ScalarSet(Telemetry::ScalarID::TELEMETRY_TEST_UNSIGNED_INT_KIND,
+                       true);
+  TelemetryScalar::ApplyPendingOperations();
+
+  JS::Rooted<JS::Value> scalarsSnapshot(cx.GetJSContext());
+  GetScalarsSnapshot(false, cx.GetJSContext(), &scalarsSnapshot);
+  CheckStringScalar("telemetry.test.string_kind", cx.GetJSContext(),
+                    scalarsSnapshot, EXPECTED_STRING);
+  CheckBoolScalar("telemetry.test.boolean_kind", cx.GetJSContext(),
+                  scalarsSnapshot, true);
+  CheckUintScalar("telemetry.test.unsigned_int_kind", cx.GetJSContext(),
+                  scalarsSnapshot, expectedValue);
+}
+
+TEST_F(TelemetryTestFixture, WrongKeyedScalarOperator) {
+  AutoJSContextWithGlobal cx(mCleanGlobal);
+
+  // Make sure we don't get scalars from other tests.
+  Unused << mTelemetry->ClearScalars();
+
+  const uint32_t kExpectedUint = 1172017;
+
+  Telemetry::ScalarSet(Telemetry::ScalarID::TELEMETRY_TEST_KEYED_UNSIGNED_INT,
+                       u"key1"_ns, kExpectedUint);
+  Telemetry::ScalarSet(Telemetry::ScalarID::TELEMETRY_TEST_KEYED_BOOLEAN_KIND,
+                       u"key2"_ns, true);
+
+  TelemetryScalar::DeserializationStarted();
+
+  Telemetry::ScalarSet(Telemetry::ScalarID::TELEMETRY_TEST_KEYED_UNSIGNED_INT,
+                       u"key1"_ns, false);
+  Telemetry::ScalarSet(Telemetry::ScalarID::TELEMETRY_TEST_KEYED_BOOLEAN_KIND,
+                       u"key2"_ns, static_cast<uint32_t>(13));
+
+  TelemetryScalar::ApplyPendingOperations();
+
+  JS::Rooted<JS::Value> scalarsSnapshot(cx.GetJSContext());
+  GetScalarsSnapshot(true, cx.GetJSContext(), &scalarsSnapshot);
+  CheckKeyedUintScalar("telemetry.test.keyed_unsigned_int", "key1",
+                       cx.GetJSContext(), scalarsSnapshot, kExpectedUint);
+  CheckKeyedBoolScalar("telemetry.test.keyed_boolean_kind", "key2",
+                       cx.GetJSContext(), scalarsSnapshot, true);
+}
+
+TEST_F(TelemetryTestFixture, TestKeyedScalarAllowedKeys) {
+  AutoJSContextWithGlobal cx(mCleanGlobal);
+  // Make sure we don't get scalars from other tests.
+  Unused << mTelemetry->ClearScalars();
+
+  const uint32_t kExpectedUint = 1172017;
+
+  Telemetry::ScalarSet(Telemetry::ScalarID::TELEMETRY_TEST_KEYED_WITH_KEYS,
+                       u"only"_ns, kExpectedUint);
+  Telemetry::ScalarSet(Telemetry::ScalarID::TELEMETRY_TEST_KEYED_WITH_KEYS,
+                       u"meant"_ns, kExpectedUint);
+  Telemetry::ScalarSet(Telemetry::ScalarID::TELEMETRY_TEST_KEYED_WITH_KEYS,
+                       u"for"_ns, kExpectedUint);
+  Telemetry::ScalarSet(Telemetry::ScalarID::TELEMETRY_TEST_KEYED_WITH_KEYS,
+                       u"testing"_ns, kExpectedUint);
+
+  Telemetry::ScalarSet(Telemetry::ScalarID::TELEMETRY_TEST_KEYED_WITH_KEYS,
+                       u"invalid"_ns, kExpectedUint);
+  Telemetry::ScalarSet(Telemetry::ScalarID::TELEMETRY_TEST_KEYED_WITH_KEYS,
+                       u"not-valid"_ns, kExpectedUint);
+
+  JS::Rooted<JS::Value> scalarsSnapshot(cx.GetJSContext());
+  GetScalarsSnapshot(true, cx.GetJSContext(), &scalarsSnapshot);
+  CheckKeyedUintScalar("telemetry.test.keyed_with_keys", "only",
+                       cx.GetJSContext(), scalarsSnapshot, kExpectedUint);
+  CheckKeyedUintScalar("telemetry.test.keyed_with_keys", "meant",
+                       cx.GetJSContext(), scalarsSnapshot, kExpectedUint);
+  CheckKeyedUintScalar("telemetry.test.keyed_with_keys", "for",
+                       cx.GetJSContext(), scalarsSnapshot, kExpectedUint);
+  CheckKeyedUintScalar("telemetry.test.keyed_with_keys", "testing",
+                       cx.GetJSContext(), scalarsSnapshot, kExpectedUint);
+  CheckNumberOfProperties("telemetry.test.keyed_with_keys", cx.GetJSContext(),
+                          scalarsSnapshot, 4);
+
+  CheckKeyedUintScalar("telemetry.keyed_scalars_unknown_keys",
+                       "telemetry.test.keyed_with_keys", cx.GetJSContext(),
+                       scalarsSnapshot, 2);
+}
+
+// Test that we can properly handle too long key.
+TEST_F(TelemetryTestFixture, TooLongKey) {
+  AutoJSContextWithGlobal cx(mCleanGlobal);
+
+  // Make sure we don't get scalars from other tests.
+  Unused << mTelemetry->ClearScalars();
+
+// Don't run this part in debug builds as that intentionally asserts.
+#ifndef DEBUG
+  const char* kScalarName = "telemetry.test.keyed_unsigned_int";
+  const uint32_t kKey1Value = 1172015;
+
+  Telemetry::ScalarSet(Telemetry::ScalarID::TELEMETRY_TEST_KEYED_UNSIGNED_INT,
+                       u"123456789012345678901234567890123456789012345678901234"
+                       u"5678901234567890morethanseventy"_ns,
+                       kKey1Value);
+
+  const uint32_t kDummyUint = 1172017;
+
+  // add dummy value so that object can be created from snapshot
+  Telemetry::ScalarSet(Telemetry::ScalarID::TELEMETRY_TEST_KEYED_WITH_KEYS,
+                       u"dummy"_ns, kDummyUint);
+  // Check the recorded value
+  JS::Rooted<JS::Value> scalarsSnapshot(cx.GetJSContext());
+  GetScalarsSnapshot(true, cx.GetJSContext(), &scalarsSnapshot);
+
+  bool foundp = true;
+  JS::Rooted<JSObject*> scalarObj(cx.GetJSContext(),
+                                  &scalarsSnapshot.toObject());
+  ASSERT_TRUE(
+      JS_HasProperty(cx.GetJSContext(), scalarObj, kScalarName, &foundp));
+  EXPECT_FALSE(foundp);
+#endif  // #ifndef DEBUG
+}
+
+// Test that we can properly handle empty key
+TEST_F(TelemetryTestFixture, EmptyKey) {
+  AutoJSContextWithGlobal cx(mCleanGlobal);
+
+  // Make sure we don't get scalars from other tests.
+  Unused << mTelemetry->ClearScalars();
+
+// Don't run this part in debug builds as that intentionally asserts.
+#ifndef DEBUG
+  const char* kScalarName = "telemetry.test.keyed_unsigned_int";
+  const uint32_t kKey1Value = 1172015;
+
+  Telemetry::ScalarSet(Telemetry::ScalarID::TELEMETRY_TEST_KEYED_UNSIGNED_INT,
+                       u""_ns, kKey1Value);
+
+  const uint32_t kDummyUint = 1172017;
+
+  // add dummy value so that object can be created from snapshot
+  Telemetry::ScalarSet(Telemetry::ScalarID::TELEMETRY_TEST_KEYED_WITH_KEYS,
+                       u"dummy"_ns, kDummyUint);
+
+  // Check the recorded value
+  JS::Rooted<JS::Value> scalarsSnapshot(cx.GetJSContext());
+  GetScalarsSnapshot(true, cx.GetJSContext(), &scalarsSnapshot);
+
+  bool foundp = true;
+  JS::Rooted<JSObject*> scalarObj(cx.GetJSContext(),
+                                  &scalarsSnapshot.toObject());
+  ASSERT_TRUE(
+      JS_HasProperty(cx.GetJSContext(), scalarObj, kScalarName, &foundp));
+  EXPECT_FALSE(foundp);
+#endif  // #ifndef DEBUG
+}
+
+// Test that we can properly handle too many keys
+TEST_F(TelemetryTestFixture, TooManyKeys) {
+  AutoJSContextWithGlobal cx(mCleanGlobal);
+
+  // Make sure we don't get scalars from other tests.
+  Unused << mTelemetry->ClearScalars();
+
+// Don't run this part in debug builds as that intentionally asserts.
+#ifndef DEBUG
+  const char* kScalarName = "telemetry.test.keyed_unsigned_int";
+  const uint32_t kKey1Value = 1172015;
+
+  for (int i = 0; i < 150; i++) {
+    std::u16string key = u"key";
+    char16_t n = i + '0';
+    key.push_back(n);
+    Telemetry::ScalarSet(Telemetry::ScalarID::TELEMETRY_TEST_KEYED_UNSIGNED_INT,
+                         nsString(key.c_str()), kKey1Value);
+  }
+
+  // Check the recorded value
+  JS::Rooted<JS::Value> scalarsSnapshot(cx.GetJSContext());
+  GetScalarsSnapshot(true, cx.GetJSContext(), &scalarsSnapshot);
+
+  // Check 100 keys are present.
+  CheckNumberOfProperties(kScalarName, cx.GetJSContext(), scalarsSnapshot, 100);
+#endif  // #ifndef DEBUG
+}
diff --git a/toolkit/components/telemetry/tests/gtest/moz.build b/toolkit/components/telemetry/tests/gtest/moz.build
new file mode 100644
index 0000000000..cdf67dc63d
--- /dev/null
+++ b/toolkit/components/telemetry/tests/gtest/moz.build
@@ -0,0 +1,29 @@
+# -*- Mode: python; c-basic-offset: 4; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, you can obtain one at http://mozilla.org/MPL/2.0/.
+
+Library("telemetrytest")
+
+LOCAL_INCLUDES += [
+    "../..",
+]
+
+UNIFIED_SOURCES = [
+    "TelemetryFixture.cpp",
+    "TelemetryTestHelpers.cpp",
+]
+
+if CONFIG["OS_TARGET"] != "Android":
+    UNIFIED_SOURCES += [
+        "TestCombinedStacks.cpp",
+        "TestCounters.cpp",
+        "TestEvents.cpp",
+        "TestHistograms.cpp",
+        "TestScalars.cpp",
+    ]
+
+FINAL_LIBRARY = "xul-gtest"
+
+include("/ipc/chromium/chromium-config.mozbuild")