refactor(jest-mock)!: simplify usage of jest.fn generic type arguments

CHANGELOG.md

@@ -20,8 +20,9 @@
 - `[jest-environment-node]` [**BREAKING**] Second argument `context` to constructor is mandatory ([#12469](https://github.com/facebook/jest/pull/12469))
 - `[@jest/expect]` New module which extends `expect` with `jest-snapshot` matchers ([#12404](https://github.com/facebook/jest/pull/12404), [#12410](https://github.com/facebook/jest/pull/12410), [#12418](https://github.com/facebook/jest/pull/12418))
 - `[@jest/expect-utils]` New module exporting utils for `expect` ([#12323](https://github.com/facebook/jest/pull/12323))
-- `[jest-mock]` [**BREAKING**] Rename exported utility types `ConstructorLike`, `MethodLike`, `ConstructorLikeKeys`, `MethodLikeKeys`, `PropertyLikeKeys`; remove exports of utility types `ArgumentsOf`, `ArgsType`, `ConstructorArgumentsOf` - TS builtin utility types `ConstructorParameters` and `Parameters` should be used instead ([#12435](https://github.com/facebook/jest/pull/12435))
+- `[jest-mock]` [**BREAKING**] Rename exported utility types `ClassLike`, `FunctionLike`, `ConstructorLikeKeys`, `MethodLikeKeys`, `PropertyLikeKeys`; remove exports of utility types `ArgumentsOf`, `ArgsType`, `ConstructorArgumentsOf` - TS builtin utility types `ConstructorParameters` and `Parameters` should be used instead ([#12435](https://github.com/facebook/jest/pull/12435), [#12489](https://github.com/facebook/jest/pull/12489))
 - `[jest-mock]` Improve `isMockFunction` to infer types of passed function ([#12442](https://github.com/facebook/jest/pull/12442))
+- `[jest-mock]` [**BREAKING**] Improve the usage of `jest.fn` generic type argument ([#12489](https://github.com/facebook/jest/pull/12489))
 - `[jest-resolve]` [**BREAKING**] Add support for `package.json` `exports` ([#11961](https://github.com/facebook/jest/pull/11961), [#12373](https://github.com/facebook/jest/pull/12373))
 - `[jest-resolve, jest-runtime]` Add support for `data:` URI import and mock ([#12392](https://github.com/facebook/jest/pull/12392))
 - `[jest-resolve, jest-runtime]` Add support for async resolver ([#11540](https://github.com/facebook/jest/pull/11540))

docs/JestObjectAPI.md

@@ -453,7 +453,7 @@ const otherCopyOfMyModule = require('myModule');
 
 ## Mock Functions
 
-### `jest.fn(implementation)`
+### `jest.fn(implementation?)`
 
 Returns a new, unused [mock function](MockFunctionAPI.md). Optionally takes a mock implementation.
 
@@ -467,6 +467,12 @@ const returnsTrue = jest.fn(() => true);
 console.log(returnsTrue()); // true;
 ```
 
+:::note
+
+See [Mock Functions](MockFunctionAPI.md#jestfnimplementation) page for details on TypeScript usage.
+
+:::
+
 ### `jest.isMockFunction(fn)`
 
 Determines if the given function is a mocked function.