message: Add test for duplicate events
diff: @@ -29,6 +29,19 @@ describe("Emitter", () => {
  emitter.dispose();
  });
  + it("can unbind duplicate events", () => {
  + const emitter = new Emitter();
  + const callback = () => {
  + throw new Error("should call this");
  + };
  + emitter.on("something", callback);
  + emitter.on("something", callback);
  + emitter.on("something", callback);
  + emitter.off("something", callback);
  + emitter.emit("something");
  + emitter.dispose();
  + });
  +
  it("'off' does nothing if there is no event scheduled", () => {
  const emitter = new Emitter();
  const callback = () => {
  