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diff --git a/devtools/shared/tests/xpcshell/test_eventemitter_basic.js b/devtools/shared/tests/xpcshell/test_eventemitter_basic.js
new file mode 100644
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+++ b/devtools/shared/tests/xpcshell/test_eventemitter_basic.js
@@ -0,0 +1,345 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+const {
+  ConsoleAPIListener,
+} = require("resource://devtools/server/actors/webconsole/listeners/console-api.js");
+const EventEmitter = require("resource://devtools/shared/event-emitter.js");
+const hasMethod = (target, method) =>
+  method in target && typeof target[method] === "function";
+
+/**
+ * Each method of this object is a test; tests can be synchronous or asynchronous:
+ *
+ * 1. Plain functions are synchronous tests.
+ * 2. methods with `async` keyword are asynchronous tests.
+ * 3. methods with `done` as argument are asynchronous tests (`done` needs to be called to
+ *    finish the test).
+ */
+const TESTS = {
+  testEventEmitterCreation() {
+    const emitter = getEventEmitter();
+    const isAnEmitter = emitter instanceof EventEmitter;
+
+    ok(emitter, "We have an event emitter");
+    ok(
+      hasMethod(emitter, "on") &&
+        hasMethod(emitter, "off") &&
+        hasMethod(emitter, "once") &&
+        hasMethod(emitter, "count") &&
+        !hasMethod(emitter, "decorate"),
+      `Event Emitter ${
+        isAnEmitter ? "instance" : "mixin"
+      } has the expected methods.`
+    );
+  },
+
+  testEmittingEvents(done) {
+    const emitter = getEventEmitter();
+
+    let beenHere1 = false;
+    let beenHere2 = false;
+
+    function next(str1, str2) {
+      equal(str1, "abc", "Argument 1 is correct");
+      equal(str2, "def", "Argument 2 is correct");
+
+      ok(!beenHere1, "first time in next callback");
+      beenHere1 = true;
+
+      emitter.off("next", next);
+
+      emitter.emit("next");
+
+      emitter.once("onlyonce", onlyOnce);
+
+      emitter.emit("onlyonce");
+      emitter.emit("onlyonce");
+    }
+
+    function onlyOnce() {
+      ok(!beenHere2, '"once" listener has been called once');
+      beenHere2 = true;
+      emitter.emit("onlyonce");
+
+      done();
+    }
+
+    emitter.on("next", next);
+    emitter.emit("next", "abc", "def");
+  },
+
+  testThrowingExceptionInListener(done) {
+    const emitter = getEventEmitter();
+    const listener = new ConsoleAPIListener(null, message => {
+      equal(message.level, "error");
+      const [arg] = message.arguments;
+      equal(arg.message, "foo");
+      equal(arg.stack, "bar");
+      listener.destroy();
+      done();
+    });
+
+    listener.init();
+
+    function throwListener() {
+      emitter.off("throw-exception");
+      const err = new Error("foo");
+      err.stack = "bar";
+      throw err;
+    }
+
+    emitter.on("throw-exception", throwListener);
+    emitter.emit("throw-exception");
+  },
+
+  testKillItWhileEmitting(done) {
+    const emitter = getEventEmitter();
+
+    const c1 = () => ok(true, "c1 called");
+    const c2 = () => {
+      ok(true, "c2 called");
+      emitter.off("tick", c3);
+    };
+    const c3 = () => ok(false, "c3 should not be called");
+    const c4 = () => {
+      ok(true, "c4 called");
+      done();
+    };
+
+    emitter.on("tick", c1);
+    emitter.on("tick", c2);
+    emitter.on("tick", c3);
+    emitter.on("tick", c4);
+
+    emitter.emit("tick");
+  },
+
+  testOffAfterOnce() {
+    const emitter = getEventEmitter();
+
+    let enteredC1 = false;
+    const c1 = () => (enteredC1 = true);
+
+    emitter.once("oao", c1);
+    emitter.off("oao", c1);
+
+    emitter.emit("oao");
+
+    ok(!enteredC1, "c1 should not be called");
+  },
+
+  testPromise() {
+    const emitter = getEventEmitter();
+    const p = emitter.once("thing");
+
+    // Check that the promise is only resolved once event though we
+    // emit("thing") more than once
+    let firstCallbackCalled = false;
+    const check1 = p.then(arg => {
+      equal(firstCallbackCalled, false, "first callback called only once");
+      firstCallbackCalled = true;
+      equal(arg, "happened", "correct arg in promise");
+      return "rval from c1";
+    });
+
+    emitter.emit("thing", "happened", "ignored");
+
+    // Check that the promise is resolved asynchronously
+    let secondCallbackCalled = false;
+    const check2 = p.then(arg => {
+      ok(true, "second callback called");
+      equal(arg, "happened", "correct arg in promise");
+      secondCallbackCalled = true;
+      equal(arg, "happened", "correct arg in promise (a second time)");
+      return "rval from c2";
+    });
+
+    // Shouldn't call any of the above listeners
+    emitter.emit("thing", "trashinate");
+
+    // Check that we can still separate events with different names
+    // and that it works with no parameters
+    const pfoo = emitter.once("foo");
+    const pbar = emitter.once("bar");
+
+    const check3 = pfoo.then(arg => {
+      Assert.strictEqual(arg, undefined, "no arg for foo event");
+      return "rval from c3";
+    });
+
+    pbar.then(() => {
+      ok(false, "pbar should not be called");
+    });
+
+    emitter.emit("foo");
+
+    equal(secondCallbackCalled, false, "second callback not called yet");
+
+    return Promise.all([check1, check2, check3]).then(args => {
+      equal(args[0], "rval from c1", "callback 1 done good");
+      equal(args[1], "rval from c2", "callback 2 done good");
+      equal(args[2], "rval from c3", "callback 3 done good");
+    });
+  },
+
+  testClearEvents() {
+    const emitter = getEventEmitter();
+
+    const received = [];
+    const listener = (...args) => received.push(args);
+
+    emitter.on("a", listener);
+    emitter.on("b", listener);
+    emitter.on("c", listener);
+
+    emitter.emit("a", 1);
+    emitter.emit("b", 1);
+    emitter.emit("c", 1);
+
+    equal(received.length, 3, "the listener was triggered three times");
+
+    emitter.clearEvents();
+    emitter.emit("a", 1);
+    emitter.emit("b", 1);
+    emitter.emit("c", 1);
+    equal(received.length, 3, "the listener was not called after clearEvents");
+  },
+
+  testOnReturn() {
+    const emitter = getEventEmitter();
+
+    let called = false;
+    const removeOnTest = emitter.on("test", () => {
+      called = true;
+    });
+
+    equal(typeof removeOnTest, "function", "`on` returns a function");
+    removeOnTest();
+
+    emitter.emit("test");
+    equal(called, false, "event listener wasn't called");
+  },
+
+  async testEmitAsync() {
+    const emitter = getEventEmitter();
+
+    let resolve1, resolve2;
+    emitter.once("test", async () => {
+      return new Promise(r => {
+        resolve1 = r;
+      });
+    });
+
+    // Adding a listener which doesn't return a promise should trigger a console warning.
+    emitter.once("test", () => {});
+
+    emitter.once("test", async () => {
+      return new Promise(r => {
+        resolve2 = r;
+      });
+    });
+
+    info("Emit an event and wait for all listener resolutions");
+    const onConsoleWarning = onConsoleWarningLogged(
+      "Listener for event 'test' did not return a promise."
+    );
+    const onEmitted = emitter.emitAsync("test");
+    let resolved = false;
+    onEmitted.then(() => {
+      info("emitAsync just resolved");
+      resolved = true;
+    });
+
+    info("Waiting for warning message about the second listener");
+    await onConsoleWarning;
+
+    // Spin the event loop, to ensure that emitAsync did not resolved too early
+    await new Promise(r => Services.tm.dispatchToMainThread(r));
+
+    ok(resolve1, "event listener has been called");
+    ok(!resolved, "but emitAsync hasn't resolved yet");
+
+    info("Resolve the first listener function");
+    resolve1();
+    ok(!resolved, "emitAsync isn't resolved until all listener resolve");
+
+    info("Resolve the second listener function");
+    resolve2();
+
+    // emitAsync is only resolved in the next event loop
+    await new Promise(r => Services.tm.dispatchToMainThread(r));
+    ok(resolved, "once we resolve all the listeners, emitAsync is resolved");
+  },
+
+  testCount() {
+    const emitter = getEventEmitter();
+
+    equal(emitter.count("foo"), 0, "no listeners for 'foo' events");
+    emitter.on("foo", () => {});
+    equal(emitter.count("foo"), 1, "listener registered");
+    emitter.on("foo", () => {});
+    equal(emitter.count("foo"), 2, "another listener registered");
+    emitter.off("foo");
+    equal(emitter.count("foo"), 0, "listeners unregistered");
+  },
+};
+
+// Wait for the next call to console.warn which includes
+// the text passed as argument
+function onConsoleWarningLogged(warningMessage) {
+  return new Promise(resolve => {
+    const ConsoleAPIStorage = Cc[
+      "@mozilla.org/consoleAPI-storage;1"
+    ].getService(Ci.nsIConsoleAPIStorage);
+
+    const observer = subject => {
+      // This is the first argument passed to console.warn()
+      const message = subject.wrappedJSObject.arguments[0];
+      if (message.includes(warningMessage)) {
+        ConsoleAPIStorage.removeLogEventListener(observer);
+        resolve();
+      }
+    };
+
+    ConsoleAPIStorage.addLogEventListener(
+      observer,
+      Cc["@mozilla.org/systemprincipal;1"].createInstance(Ci.nsIPrincipal)
+    );
+  });
+}
+
+/**
+ * Create a runnable tests based on the tests descriptor given.
+ *
+ * @param {Object} tests
+ *  The tests descriptor object, contains the tests to run.
+ */
+const runnable = tests =>
+  async function () {
+    for (const name of Object.keys(tests)) {
+      info(name);
+      if (tests[name].length === 1) {
+        await new Promise(resolve => tests[name](resolve));
+      } else {
+        await tests[name]();
+      }
+    }
+  };
+
+// We want to run the same tests for both an instance of `EventEmitter` and an object
+// decorate with EventEmitter; therefore we create two strategies (`createNewEmitter` and
+// `decorateObject`) and a factory (`getEventEmitter`), where the factory is the actual
+// function used in the tests.
+
+const createNewEmitter = () => new EventEmitter();
+const decorateObject = () => EventEmitter.decorate({});
+
+// First iteration of the tests with a new instance of `EventEmitter`.
+let getEventEmitter = createNewEmitter;
+add_task(runnable(TESTS));
+// Second iteration of the tests with an object decorate using `EventEmitter`
+add_task(() => (getEventEmitter = decorateObject));
+add_task(runnable(TESTS));