1 files changed, 48 insertions, 0 deletions
diff --git a/toolkit/components/telemetry/tests/unit/test_bug1555798.js b/toolkit/components/telemetry/tests/unit/test_bug1555798.js
new file mode 100644
index 0000000000..f5a84c200c
--- /dev/null
+++ b/toolkit/components/telemetry/tests/unit/test_bug1555798.js
@@ -0,0 +1,48 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/
+*/
+
+ChromeUtils.defineESModuleGetters(this, {
+  TelemetryTestUtils: "resource://testing-common/TelemetryTestUtils.sys.mjs",
+});
+
+add_task(async function test_bug1555798() {
+  /*
+  The idea behind this bug is that the registration of dynamic scalars causes
+  the position of the scalarinfo for telemetry.dynamic_events_count to move
+  which causes things to asplode.
+
+  So to test this we'll be registering two dynamic events, recording to one of
+  the events (to ensure the Scalar for event1 is allocated from the unmoved
+  DynamicScalarInfo&), registering several dynamic scalars to cause the
+  nsTArray of DynamicScalarInfo to realloc, and then recording to the second
+  event to make the Event Summary Scalar for event2 try to allocate from where
+  the DynamicScalarInfo used to be.
+  */
+  Telemetry.clearEvents();
+
+  const DYNAMIC_CATEGORY = "telemetry.test.dynamic.event";
+  Telemetry.registerEvents(DYNAMIC_CATEGORY, {
+    an_event: {
+      methods: ["a_method"],
+      objects: ["an_object", "another_object"],
+      record_on_release: true,
+      expired: false,
+    },
+  });
+  Telemetry.recordEvent(DYNAMIC_CATEGORY, "a_method", "an_object");
+
+  for (let i = 0; i < 100; ++i) {
+    Telemetry.registerScalars("telemetry.test.dynamic" + i, {
+      scalar_name: {
+        kind: Ci.nsITelemetry.SCALAR_TYPE_COUNT,
+        record_on_release: true,
+      },
+    });
+    Telemetry.scalarAdd("telemetry.test.dynamic" + i + ".scalar_name", 1);
+  }
+
+  Telemetry.recordEvent(DYNAMIC_CATEGORY, "a_method", "another_object");
+
+  TelemetryTestUtils.assertNumberOfEvents(2, {}, { process: "dynamic" });
+});