Add support for providing fallbackMockImplementation

Author: skovhus

README.md

@@ -141,6 +141,19 @@ expect(mockObj.deepProp(1)).toBe(3);
 expect(mockObj.deepProp.getNumber(1)).toBe(4);
 ```
 
+Can can provide a fallback mock implementation used if you do not define a return value using `calledWith`.
+
+```ts
+import { mockDeep } from 'jest-mock-extended';
+const mockObj = mockDeep<Test1>({
+    fallbackMockImplementation: () => {
+        throw new Error('please add expected return value using calledWith');
+    },
+});
+expect(() => mockObj.getNumber()).toThrowError('not mocked');
+```
+
+
 ## Available Matchers
 
 

src/CalledWithFn.ts

@@ -32,14 +32,16 @@ const checkCalledWith = <T, Y extends any[]>(calledWithStack: CalledWithStackIte
     return calledWithInstance ? calledWithInstance.calledWithFn(...actualArgs) : undefined;
 };
 
-export const calledWithFn = <T, Y extends any[]>(): CalledWithMock<T, Y> => {
-    const fn: jest.Mock<T, Y> = jest.fn();
+export const calledWithFn = <T, Y extends any[]>({
+    fallbackMockImplementation,
+}: { fallbackMockImplementation?: (...args: Y) => T } = {}): CalledWithMock<T, Y> => {
+    const fn: jest.Mock<T, Y> = jest.fn(fallbackMockImplementation);
     let calledWithStack: CalledWithStackItem<T, Y>[] = [];
 
     (fn as CalledWithMock<T, Y>).calledWith = (...args) => {
         // We create new function to delegate any interactions (mockReturnValue etc.) to for this set of args.
         // If that set of args is matched, we just call that jest.fn() for the result.
-        const calledWithFn = jest.fn();
+        const calledWithFn = jest.fn(fallbackMockImplementation);
         if (!fn.getMockImplementation()) {
             // Our original function gets a mock implementation which handles the matching
             fn.mockImplementation((...args: Y) => checkCalledWith(calledWithStack, args));

src/Mock.spec.ts

@@ -308,6 +308,32 @@ describe('jest-mock-extended', () => {
             mockObj.deepProp.getNumber(2);
             expect(mockObj.deepProp.getNumber).toHaveBeenCalledTimes(1);
         });
+
+        test('fallback mock implementation can be overridden', () => {
+            const mockObj = mockDeep<Test1>({
+                fallbackMockImplementation: () => {
+                    throw new Error('not mocked');
+                },
+            });
+            expect(() => mockObj.getNumber()).toThrowError('not mocked');
+        });
+
+        test('fallback mock implementation can be overridden while also providing a mock implementation', () => {
+            const mockObj = mockDeep<Test1>(
+                {
+                    fallbackMockImplementation: () => {
+                        throw new Error('not mocked');
+                    },
+                },
+                {
+                    getNumber: () => {
+                        return 150;
+                    },
+                }
+            );
+            expect(mockObj.getNumber()).toBe(150);
+            expect(() => mockObj.deepProp.getNumber(1)).toThrowError('not mocked');
+        });
     });
 
     describe('Deep mock support for class variables which are functions but also have nested properties and functions', () => {

src/Mock.ts

@@ -49,6 +49,7 @@ export type DeepMockProxyWithFuncPropSupport<T> = {
 
 export interface MockOpts {
     deep?: boolean;
+    fallbackMockImplementation?: (...args: any[]) => any;
 }
 
 export const mockClear = (mock: MockProxy<any>) => {
@@ -94,10 +95,17 @@ export const mockReset = (mock: MockProxy<any>) => {
     }
 };
 
-export function mockDeep<T>(opts: { funcPropSupport: true }, mockImplementation?: DeepPartial<T>): DeepMockProxyWithFuncPropSupport<T>;
+export function mockDeep<T>(
+    opts: { funcPropSupport?: true; fallbackMockImplementation?: MockOpts['fallbackMockImplementation'] },
+    mockImplementation?: DeepPartial<T>
+): DeepMockProxyWithFuncPropSupport<T>;
 export function mockDeep<T>(mockImplementation?: DeepPartial<T>): DeepMockProxy<T>;
 export function mockDeep(arg1: any, arg2?: any) {
-    return mock(arg1 && 'funcPropSupport' in arg1 ? arg2 : arg1, { deep: true });
+    const [opts, mockImplementation] =
+        typeof arg1 === 'object' && (typeof arg1.fallbackMockImplementation === 'function' || arg1.funcPropSupport === true)
+            ? [arg1, arg2]
+            : [{}, arg1];
+    return mock(mockImplementation, { deep: true, fallbackMockImplementation: opts.fallbackMockImplementation });
 }
 
 const overrideMockImp = (obj: DeepPartial<any>, opts?: MockOpts) => {
@@ -125,7 +133,7 @@ const handler = (opts?: MockOpts) => ({
     },
 
     get: (obj: MockProxy<any>, property: ProxiedProperty) => {
-        let fn = calledWithFn();
+        let fn = calledWithFn({ fallbackMockImplementation: opts?.fallbackMockImplementation });
 
         // @ts-ignore
         if (!(property in obj)) {
@@ -148,7 +156,7 @@ const handler = (opts?: MockOpts) => ({
                 obj[property]._isMockObject = true;
             } else {
                 // @ts-ignore
-                obj[property] = calledWithFn();
+                obj[property] = calledWithFn({ fallbackMockImplementation: opts?.fallbackMockImplementation });
             }
         }