Wrap mounts simulate() in ReactTestUtils.act()

Wraps the mount simulate method in ReactTestUtils.act() to correctly
allow component interactions to be tested in a synchronous way

Fixes #2084

packages/enzyme-adapter-react-16/src/ReactSixteenAdapter.js

@@ -474,7 +474,9 @@ class ReactSixteenAdapter extends EnzymeAdapter {
         if (!eventFn) {
           throw new TypeError(`ReactWrapper::simulate() event '${event}' does not exist`);
         }
-        eventFn(adapter.nodeToHostNode(node), mock);
+        wrapAct(() => {
+          eventFn(adapter.nodeToHostNode(node), mock);
+        });
       },
       batchedUpdates(fn) {
         return fn();

packages/enzyme-test-suite/test/ReactWrapper-spec.jsx

@@ -1034,6 +1034,25 @@ describeWithDOM('mount', () => {
         done();
       }, 100);
     });
+
+    it('works with `useEffect` simulated events', () => {
+      const effectSpy = sinon.spy();
+      function ComponentUsingEffectHook() {
+        useEffect(effectSpy);
+        const [counter, setCounter] = useState(0);
+
+        return (
+          <button onClick={() => setCounter(counter + 1)}>{counter}</button>
+        );
+      }
+      const wrapper = mount(<ComponentUsingEffectHook />);
+
+      const button = wrapper.find('button');
+      button.simulate('click');
+
+      expect(button.text()).to.equal('1');
+      expect(effectSpy).to.have.property('callCount', 2);
+    });
   });
 
   itIf(is('>= 16.2'), 'supports fragments', () => {