1 files changed, 110 insertions, 0 deletions
diff --git a/toolkit/components/normandy/test/browser/browser_EventEmitter.js b/toolkit/components/normandy/test/browser/browser_EventEmitter.js
new file mode 100644
index 0000000000..a64c52896f
--- /dev/null
+++ b/toolkit/components/normandy/test/browser/browser_EventEmitter.js
@@ -0,0 +1,110 @@
+"use strict";
+
+const { EventEmitter } = ChromeUtils.importESModule(
+  "resource://normandy/lib/EventEmitter.sys.mjs"
+);
+
+const evidence = {
+  a: 0,
+  b: 0,
+  c: 0,
+  log: "",
+};
+
+function listenerA(x) {
+  evidence.a += x;
+  evidence.log += "a";
+}
+
+function listenerB(x) {
+  evidence.b += x;
+  evidence.log += "b";
+}
+
+function listenerC(x) {
+  evidence.c += x;
+  evidence.log += "c";
+}
+
+decorate_task(async function () {
+  const eventEmitter = new EventEmitter();
+
+  // Fire an unrelated event, to make sure nothing goes wrong
+  eventEmitter.on("nothing");
+
+  // bind listeners
+  eventEmitter.on("event", listenerA);
+  eventEmitter.on("event", listenerB);
+  eventEmitter.once("event", listenerC);
+
+  // one event for all listeners
+  eventEmitter.emit("event", 1);
+  // another event for a and b, since c should have turned off already
+  eventEmitter.emit("event", 10);
+
+  // make sure events haven't actually fired yet, just queued
+  Assert.deepEqual(
+    evidence,
+    {
+      a: 0,
+      b: 0,
+      c: 0,
+      log: "",
+    },
+    "events are fired async"
+  );
+
+  // Spin the event loop to run events, so we can safely "off"
+  await Promise.resolve();
+
+  // Check intermediate event results
+  Assert.deepEqual(
+    evidence,
+    {
+      a: 11,
+      b: 11,
+      c: 1,
+      log: "abcab",
+    },
+    "intermediate events are fired"
+  );
+
+  // one more event for a
+  eventEmitter.off("event", listenerB);
+  eventEmitter.emit("event", 100);
+
+  // And another unrelated event
+  eventEmitter.on("nothing");
+
+  // Spin the event loop to run events
+  await Promise.resolve();
+
+  Assert.deepEqual(
+    evidence,
+    {
+      a: 111,
+      b: 11,
+      c: 1,
+      log: "abcaba", // events are in order
+    },
+    "events fired as expected"
+  );
+
+  // Test that mutating the data passed to the event doesn't actually
+  // mutate it for other events.
+  let handlerRunCount = 0;
+  const mutationHandler = data => {
+    handlerRunCount++;
+    data.count++;
+    is(data.count, 1, "Event data is not mutated between handlers.");
+  };
+  eventEmitter.on("mutationTest", mutationHandler);
+  eventEmitter.on("mutationTest", mutationHandler);
+
+  const data = { count: 0 };
+  eventEmitter.emit("mutationTest", data);
+  await Promise.resolve();
+
+  is(handlerRunCount, 2, "Mutation handler was executed twice.");
+  is(data.count, 0, "Event data cannot be mutated by handlers.");
+});