implement mockResolved/RejectedValue methods using mockImplementation (…

…#5720)

CHANGELOG.md

@@ -33,6 +33,8 @@
   ([#5670](https://github.com/facebook/jest/pull/5670))
 * `[jest-runtime]` Prevent Babel warnings on large files
   ([#5702](https://github.com/facebook/jest/pull/5702))
+* `[jest-mock]` Prevent `mockRejectedValue` from causing unhandled rejection
+  ([#5720](https://github.com/facebook/jest/pull/5720))
 
 ### Chore & Maintenance
 

docs/MockFunctionAPI.md

@@ -250,7 +250,7 @@ console.log(myMockFn(), myMockFn(), myMockFn(), myMockFn());
 Simple sugar function for:
 
 ```js
-jest.fn().mockReturnValue(Promise.resolve(value));
+jest.fn().mockImplementation(() => Promise.resolve(value));
 ```
 
 Useful to mock async functions in async tests:
@@ -270,7 +270,7 @@ test('async test', async () => {
 Simple sugar function for:
 
 ```js
-jest.fn().mockReturnValueOnce(Promise.resolve(value));
+jest.fn().mockImplementationOnce(() => Promise.resolve(value));
 ```
 
 Useful to resolve different values over multiple async calls:
@@ -297,7 +297,7 @@ test('async test', async () => {
 Simple sugar function for:
 
 ```js
-jest.fn().mockReturnValue(Promise.reject(value));
+jest.fn().mockImplementation(() => Promise.reject(value));
 ```
 
 Useful to create async mock functions that will always reject:
@@ -317,7 +317,7 @@ test('async test', async () => {
 Simple sugar function for:
 
 ```js
-jest.fn().mockReturnValueOnce(Promise.reject(value));
+jest.fn().mockImplementationOnce(() => Promise.reject(value));
 ```
 
 Example usage:

packages/jest-mock/src/index.js

@@ -227,17 +227,6 @@ function getSlots(object?: Object): Array<string> {
   return Object.keys(slots);
 }
 
-function wrapAsyncParam(
-  fn: any => any,
-  asyncAction: 'resolve' | 'reject',
-): any => any {
-  if (asyncAction === 'reject') {
-    return value => fn(Promise.reject(value));
-  }
-
-  return value => fn(Promise.resolve(value));
-}
-
 class ModuleMockerClass {
   _environmentGlobal: Global;
   _mockState: WeakMap<Function, MockFunctionState>;
@@ -418,12 +407,11 @@ class ModuleMockerClass {
         return f;
       };
 
-      f.mockResolvedValueOnce = wrapAsyncParam(
-        f.mockReturnValueOnce,
-        'resolve',
-      );
+      f.mockResolvedValueOnce = value =>
+        f.mockImplementationOnce(() => Promise.resolve(value));
 
-      f.mockRejectedValueOnce = wrapAsyncParam(f.mockReturnValueOnce, 'reject');
+      f.mockRejectedValueOnce = value =>
+        f.mockImplementationOnce(() => Promise.reject(value));
 
       f.mockReturnValue = value => {
         // next function call will return specified return value or this one
@@ -433,9 +421,11 @@ class ModuleMockerClass {
         return f;
       };
 
-      f.mockResolvedValue = wrapAsyncParam(f.mockReturnValue, 'resolve');
+      f.mockResolvedValue = value =>
+        f.mockImplementation(() => Promise.resolve(value));
 
-      f.mockRejectedValue = wrapAsyncParam(f.mockReturnValue, 'reject');
+      f.mockRejectedValue = value =>
+        f.mockImplementation(() => Promise.reject(value));
 
       f.mockImplementationOnce = fn => {
         // next function call will use this mock implementation return value