Should not rely on synchronous return value of renderIntoDocument

.babelrc

@@ -4,6 +4,7 @@
   "plugins": [
     "fbjs-scripts/babel-6/dev-expression",
     "syntax-trailing-function-commas",
+    "babel-plugin-transform-async-to-generator",
     "babel-plugin-transform-object-rest-spread",
     "transform-es2015-template-literals",
     "transform-es2015-literals",

package.json

@@ -101,5 +101,9 @@
     "unmockedModulePathPatterns": [
       ""
     ]
+  },
+  "dependencies": {
+    "babel-plugin-syntax-async-functions": "^6.8.0",
+    "babel-plugin-transform-async-to-generator": "^6.8.0"
   }
 }

src/test/ReactTestUtils.js

@@ -80,14 +80,38 @@ function findAllInRenderedTreeInternal(inst, test) {
  * @lends ReactTestUtils
  */
 var ReactTestUtils = {
-  renderIntoDocument: function(instance) {
+  renderIntoDocument: function(element) {
     var div = document.createElement('div');
     // None of our tests actually require attaching the container to the
     // DOM, and doing so creates a mess that we rely on test isolation to
     // clean up, so we're going to stop honoring the name of this method
     // (and probably rename it eventually) if no problems arise.
     // document.documentElement.appendChild(div);
-    return ReactDOM.render(instance, div);
+    return ReactDOM.render(element, div);
+  },
+
+  renderIntoDocumentAsync: function(element) {
+    invariant(typeof element.ref !== 'string',
+      'String refs can not be used at the top-level element of a render.'
+    );
+    var promise = new Promise(function(fulfill, reject) {
+      var div = document.createElement('div');
+      // None of our tests actually require attaching the container to the
+      // DOM, and doing so creates a mess that we rely on test isolation to
+      // clean up, so we're going to stop honoring the name of this method
+      // (and probably rename it eventually) if no problems arise.
+      // document.documentElement.appendChild(div);
+      var oldRef = element.ref;
+      var newRef = (instance) => {
+        if (oldRef) {
+          oldRef(instance);
+        }
+        fulfill(instance);
+      };
+      element = React.cloneElement(element, {ref: newRef});
+      ReactDOM.render(element, div);
+    });
+    return promise;
   },
 
   isElement: function(element) {

src/test/__tests__/ReactTestUtils-test.js

@@ -535,4 +535,29 @@ describe('ReactTestUtils', function() {
     expect(hrs.length).toBe(2);
   });
 
+  pit('will reject string refs in renderIntoDocumentAsync', async function() {
+    try {
+      // String refs are illegal at the top level.
+      await ReactTestUtils.renderIntoDocumentAsync(<div ref="foo" />);
+      fail('this code should not be reachable');
+    } catch (e) {
+      expect(e.message).toBe('String refs can not be used at the top-level element of a render.');
+    }
+  });
+
+  pit('will fire a callback ref in renderIntoDocumentAsync', async function() {
+    var count = 0;
+    function ref(instance) {
+      count++;
+      expect(instance.tagName).toBe('DIV');
+    }
+    var instance = await ReactTestUtils.renderIntoDocumentAsync(<div ref={ref} />);
+    expect(instance.tagName).toBe('DIV');
+    expect(count).toBe(1);
+  });
+
+  pit('will not die if no ref in renderIntoDocumentAsync', async function() {
+    var instance = await ReactTestUtils.renderIntoDocumentAsync(<div />);
+    expect(instance.tagName).toBe('DIV');
+  });
 });