Merge pull request #2259 from micalevisk/patch-1

docs(fundamentals): clarify the source of `ModuleMocker` class

Author: kamilmysliwiec

content/fundamentals/unit-testing.md

@@ -165,6 +165,9 @@ Instead of using the production version of any provider, you can override it wit
 Nest also allows you to define a mock factory to apply to all of your missing dependencies. This is useful for cases where you have a large number of dependencies in a class and mocking all of them will take a long time and a lot of setup. To make use of this feature, the `createTestingModule()` will need to be chained up with the `useMocker()` method, passing a factory for your dependency mocks. This factory can take in an optional token, which is an instance token, any token which is valid for a Nest provider, and returns a mock implementation. The below is an example of creating a generic mocker using [`jest-mock`](https://www.npmjs.com/package/jest-mock) and a specific mock for `CatsService` using `jest.fn()`.
 
 ```typescript
+// ...
+import { ModuleMocker } from 'jest-mock';
+
 const moduleMocker = new ModuleMocker(global);
 
 describe('CatsController', () => {