Add a test verifying undefined key and ref are ignored

It currently fails in `createElement` because of #6879 which was introduced in #5744.
It also fails in `cloneElement` because the code with that bug was extracted and shared in 94d0dc68c8.

src/isomorphic/classic/element/__tests__/ReactElement-test.js

@@ -170,23 +170,26 @@ describe('ReactElement', function() {
     expect(element.props).toEqual(expectation);
   });
 
-  it('should not extract key and ref getters from the config when creating an element', function() {
+  it('extracts null key and ref values when creating an element', function() {
+    var element = React.createFactory(ComponentClass)({
+      key: null,
+      ref: null,
+      foo: '12',
+    });
+    expect(element.type).toBe(ComponentClass);
+    expect(element.key).toBe('null');
+    expect(element.ref).toBe(null);
+    var expectation = {foo: '12'};
+    Object.freeze(expectation);
+    expect(element.props).toEqual(expectation);
+  });
+
+  it('ignores undefined key and ref when creating an element', function() {
     var props = {
       foo: '56',
+      key: undefined,
+      ref: undefined,
     };
-
-    Object.defineProperty(props, 'key', {
-      get: function() {
-        return '12';
-      },
-    });
-
-    Object.defineProperty(props, 'ref', {
-      get: function() {
-        return '34';
-      },
-    });
-
     var element = React.createFactory(ComponentClass)(props);
     expect(element.type).toBe(ComponentClass);
     expect(element.key).toBe(null);
@@ -196,29 +199,48 @@ describe('ReactElement', function() {
     expect(element.props).toEqual(expectation);
   });
 
-  it('should not extract key and ref getters from the config when cloning an element', function() {
+  it('ignores key and ref getters when creating an element', function() {
+    var props = {
+      foo: '56',
+    };
+    Object.defineProperty(props, 'key', {
+      get: function() {
+        return '12';
+      },
+    });
+    Object.defineProperty(props, 'ref', {
+      get: function() {
+        return '34';
+      },
+    });
+    var element = React.createFactory(ComponentClass)(props);
+    expect(element.type).toBe(ComponentClass);
+    expect(element.key).toBe(null);
+    expect(element.ref).toBe(null);
+    var expectation = {foo: '56'};
+    Object.freeze(expectation);
+    expect(element.props).toEqual(expectation);
+  });
+
+  it('ignores key and ref getters when cloning an element', function() {
     var element = React.createFactory(ComponentClass)({
       key: '12',
       ref: '34',
       foo: '56',
     });
-
     var props = {
       foo: 'ef',
     };
-
     Object.defineProperty(props, 'key', {
       get: function() {
         return 'ab';
       },
     });
-
     Object.defineProperty(props, 'ref', {
       get: function() {
         return 'cd';
       },
     });
-
     var clone = React.cloneElement(element, props);
     expect(clone.type).toBe(ComponentClass);
     expect(clone.key).toBe('12');
@@ -228,19 +250,37 @@ describe('ReactElement', function() {
     expect(clone.props).toEqual(expectation);
   });
 
-  it('should allow null key and ref values when cloning an element', function() {
+  it('ignores undefined key and ref values when cloning an element', function() {
     var element = React.createFactory(ComponentClass)({
       key: '12',
       ref: '34',
       foo: '56',
     });
+    var props = {
+      key: undefined,
+      ref: undefined,
+      foo: 'ef',
+    };
+    var clone = React.cloneElement(element, props);
+    expect(clone.type).toBe(ComponentClass);
+    expect(clone.key).toBe('12');
+    expect(clone.ref).toBe('34');
+    var expectation = {foo: 'ef'};
+    Object.freeze(expectation);
+    expect(clone.props).toEqual(expectation);
+  });
 
+  it('extracts null key and ref values when cloning an element', function() {
+    var element = React.createFactory(ComponentClass)({
+      key: '12',
+      ref: '34',
+      foo: '56',
+    });
     var props = {
       key: null,
       ref: null,
       foo: 'ef',
     };
-
     var clone = React.cloneElement(element, props);
     expect(clone.type).toBe(ComponentClass);
     expect(clone.key).toBe('null');