Add regression test for facebook#18497 (facebook#18538)

sophiebits · web-flow · commit e9c1445ba09a · 2020-06-30T12:09:05.000+01:00
diff --git a/packages/react-reconciler/src/__tests__/ReactHooksWithNoopRenderer-test.js b/packages/react-reconciler/src/__tests__/ReactHooksWithNoopRenderer-test.js
@@ -3314,4 +3314,44 @@ describe('ReactHooksWithNoopRenderer', () => {
     });
     expect(ReactNoop).toMatchRenderedOutput('ABC');
   });
+
+  it('keeps intermediate state updates (issue #18497)', () => {
+    let _dispatch;
+    function Counter() {
+      const [list, dispatch] = React.useReducer((l, c) => l.concat([c]), []);
+      _dispatch = dispatch;
+
+      const json = JSON.stringify(list);
+      Scheduler.unstable_yieldValue('Render ' + json);
+      useLayoutEffect(() => {
+        Scheduler.unstable_yieldValue('Commit ' + json);
+      });
+
+      return json;
+    }
+
+    act(() => {
+      ReactNoop.render(<Counter />);
+      expect(Scheduler).toFlushAndYieldThrough(['Render []', 'Commit []']);
+      expect(ReactNoop).toMatchRenderedOutput('[]');
+    });
+
+    act(() => {
+      _dispatch(1);
+      expect(Scheduler).toFlushAndYieldThrough(['Render [1]']);
+
+      _dispatch(2);
+      expect(Scheduler).toFlushAndYieldThrough(['Commit [1]']);
+      expect(ReactNoop).toMatchRenderedOutput('[1]');
+
+      expect(Scheduler).toFlushAndYieldThrough(['Render [1,2]']);
+      _dispatch(3);
+
+      expect(Scheduler).toFlushAndYieldThrough([
+        'Render [1,2,3]',
+        'Commit [1,2,3]',
+      ]);
+      expect(ReactNoop).toMatchRenderedOutput('[1,2,3]');
+    });
+  });
 });
diff --git a/scripts/jest/matchers/schedulerTestMatchers.js b/scripts/jest/matchers/schedulerTestMatchers.js
@@ -20,7 +20,9 @@ function assertYieldsWereCleared(Scheduler) {
   const actualYields = Scheduler.unstable_clearYields();
   if (actualYields.length !== 0) {
     throw new Error(
-      'Log of yielded values is not empty. ' +
+      'Log of yielded values is not empty: ' +
+        JSON.stringify(actualYields) +
+        '. ' +
         'Call expect(Scheduler).toHaveYielded(...) first.'
     );
   }
