Make the getMockImplementation() in Mocker module as a public method. (jestjs#1244)

Author: kunhanle

packages/jest-haste-map/src/__tests__/index-test.js

@@ -445,8 +445,7 @@ describe('HasteMap', () => {
 
   it('ignores files that do not exist', () => {
     const watchman = require('../crawlers/watchman');
-    // getMockImplementation should be a public method.
-    const mockImpl = watchman._getMockImplementation();
+    const mockImpl = watchman.getMockImplementation();
     // Wrap the watchman mock and add an invalid file to the file list.
     watchman.mockImplementation((roots, extensions, ignore, data) => {
       return mockImpl(roots, extensions, ignore, data).then(() => {

packages/jest-mock/src/__tests__/jest-mock-test.js

@@ -124,6 +124,19 @@ describe('moduleMocker', () => {
     });
   });
 
+  describe('getMockImplementation', () => {
+    it('should mock calls to a mock function', () => {
+      const mockFn = moduleMocker.getMockFunction();
+
+      mockFn.mockImplementation(() => {
+        return 'Foo';
+      });
+
+      expect(typeof mockFn.getMockImplementation()).toBe('function');
+      expect(mockFn.getMockImplementation()()).toBe('Foo');
+    });
+  });
+  
   describe('mockImplementationOnce', () => {
     it('should mock single call to a mock function', () => {
       const mockFn = moduleMocker.getMockFunction();

packages/jest-mock/src/index.js

@@ -271,7 +271,7 @@ function makeComponent(metadata: MockFunctionMetadata): Mock {
 
     f = createMockFunction(metadata, mockConstructor);
     f._isMockFunction = true;
-    f._getMockImplementation = () => mockImpl;
+    f.getMockImplementation = () => mockImpl;
     f.mock = {calls, instances};
 
     f.mockClear = () => {
@@ -389,7 +389,7 @@ function getMetadata(
   } else if (type === 'function') {
     metadata.name = component.name;
     if (component._isMockFunction) {
-      metadata.mockImpl = component._getMockImplementation();
+      metadata.mockImpl = component.getMockImplementation();
     }
   }