AndrewRayCode · September 4, 2018 01:43 · Sep 4, 2018
diff --git a/async.willmount.test.js b/async.willmount.test.js
@@ -0,0 +1,19 @@
+import { spy } from 'sinon';
+import { shallow } from 'enzyme';
+
+// Utility method to asynchronously wait for component's willMount function to
+// complete. Requires the componentWillMount method *returns* its async promise
+// to wait for
+export const willMount = async unmountedComponent => {
+  // Spy on the willmount method
+  const lifecycleMethod = spy(unmountedComponent.type.prototype, 'componentWillMount');
+  const wrapper = shallow(unmountedComponent);
+
+  // Wait for the return value of the spy (the promise returned in
+  // componentWillMount) and then undo the mock
+  await lifecycleMethod.returnValues[0];
+  lifecycleMethod.restore();
+
+  // Update component so async changes take place
+  return wrapper.update();
+};
diff --git a/usage.js b/usage.js
@@ -0,0 +1,12 @@
+class MyComponent extends Component {
+  // Note you have to *return* the promise from your lifecycle method
+  componentWillMount() {
+   return new Promise(function(resolve) { 
+       setTimeout(resolve, 100);
+   });
+  }
+}
+
+it('waits for the mount', async () => {
+  const wrapper = await willMount(<MyComponent ... />);
+});