diff --git a/js/emitter.test.js b/js/emitter.test.js
new file mode 100644
index 00000000..5cb9170b
--- /dev/null
+++ b/js/emitter.test.js
@@ -0,0 +1,53 @@
+import Emitter from "./emitter";
+
+describe("Emitter", () => {
+  it("calls a callback", () => {
+    const mock = jest.fn();
+    const emitter = new Emitter();
+    emitter.on("some-event", mock);
+    emitter.trigger("some-event");
+    expect(mock).toHaveBeenCalled();
+  });
+  it("calls multiple callbacks", () => {
+    const mock1 = jest.fn();
+    const mock2 = jest.fn();
+    const emitter = new Emitter();
+    emitter.on("some-event", mock1);
+    emitter.on("some-event", mock2);
+    emitter.trigger("some-event");
+    expect(mock1).toHaveBeenCalled();
+    expect(mock2).toHaveBeenCalled();
+  });
+  it("returns an unsubscribe function", () => {
+    const mock = jest.fn();
+    const emitter = new Emitter();
+    const unsubscribe = emitter.on("some-event", mock);
+    emitter.trigger("some-event");
+    unsubscribe();
+    emitter.trigger("some-event");
+    emitter.trigger("some-event");
+    emitter.trigger("some-event");
+    emitter.trigger("some-event");
+    emitter.trigger("some-event");
+    expect(mock).toHaveBeenCalledTimes(1);
+  });
+  it("subscriptions do not take effent until the next event", () => {
+    const mock = jest.fn();
+    const emitter = new Emitter();
+    emitter.on("some-event", () => {
+      emitter.on("some-event", mock);
+    });
+    emitter.trigger("some-event");
+    expect(mock).not.toHaveBeenCalled();
+  });
+  it("unsubscribe does not take effect until the next event", () => {
+    const mock = jest.fn();
+    const emitter = new Emitter();
+    emitter.on("some-event", () => {
+      unsubscribe(); // eslint-disable-line no-use-before-define
+    });
+    const unsubscribe = emitter.on("some-event", mock);
+    emitter.trigger("some-event");
+    expect(mock).toHaveBeenCalled();
+  });
+});