Revert "Remove undocumented TestUtils methods (facebook#10681)"

This reverts commit 18d6cb5.

Author: danseethaler

src/renderers/dom/test/ReactTestUtilsEntry.js

@@ -178,6 +178,38 @@ var ReactTestUtils = {
     return constructor === type;
   },
 
+  // TODO: deprecate? It's undocumented and unused.
+  isCompositeComponentElement: function(inst) {
+    if (!React.isValidElement(inst)) {
+      return false;
+    }
+    // We check the prototype of the type that will get mounted, not the
+    // instance itself. This is a future proof way of duck typing.
+    var prototype = inst.type.prototype;
+    return (
+      typeof prototype.render === 'function' &&
+      typeof prototype.setState === 'function'
+    );
+  },
+
+  // TODO: deprecate? It's undocumented and unused.
+  isCompositeComponentElementWithType: function(inst, type) {
+    var internalInstance = ReactInstanceMap.get(inst);
+    var constructor = internalInstance._currentElement.type;
+
+    return !!(ReactTestUtils.isCompositeComponentElement(inst) &&
+      constructor === type);
+  },
+
+  // TODO: deprecate? It's undocumented and unused.
+  getRenderedChildOfCompositeComponent: function(inst) {
+    if (!ReactTestUtils.isCompositeComponent(inst)) {
+      return null;
+    }
+    var internalInstance = ReactInstanceMap.get(inst);
+    return internalInstance._renderedComponent.getPublicInstance();
+  },
+
   findAllInRenderedTree: function(inst, test) {
     if (!inst) {
       return [];