Are there any specific libraries that simplify mocking internal functions in TypeScript

1. ts-auto-mock: This library provides a way to automatically generate mocks for TypeScript classes, interfaces, and functions. It can handle mocking internal functions as well.

Example usage:

typescript
import { mock, instance } from 'ts-auto-mock';
import { MyClass } from './my-class';

test('mocks internal function', () => {
  const myClassMock = mock(MyClass);
  myClassMock.internalFunction.mockReturnValue('mocked result');

  const myClassInstance = instance(myClassMock);
  const result = myClassInstance.publicMethod();
  expect(result).toBe('mocked result');
  expect(myClassMock.internalFunction).toHaveBeenCalled();
});

2. typemoq: This library provides a fluent API for creating mocks, stubs, and expectations in TypeScript. It can be used to mock internal functions as well.

Example usage:

typescript
import * as TypeMoq from 'typemoq';
import { MyClass } from './my-class';

test('mocks internal function', () => {
  const myClassMock = TypeMoq.Mock.ofType<MyClass>();
  myClassMock.setup(x => x.internalFunction()).returns(() => 'mocked result');

  const myClassInstance = myClassMock.object;
  const result = myClassInstance.publicMethod();
  TypeMoq.Times.once().verify(myClassMock.object.internalFunction(), TypeMoq.Times.once());
  expect(result).toBe('mocked result');
});

3. jest-mock-extended: This is a Jest-specific library that provides a set of utility functions for creating mocks, spies, and stubs in TypeScript. It can be used to mock internal functions as well.

Example usage:

typescript
import { mock, MockProxy, MockedObject } from 'jest-mock-extended';
import { MyClass } from './my-class';

test('mocks internal function', () => {
  const myClassMock: MockProxy<MyClass> = mock<MyClass>();
  myClassMock.internalFunction.mockReturnValue('mocked result');

  const myClassInstance: MockedObject<MyClass> = myClassMock;
  const result = myClassInstance.publicMethod();
  expect(myClassMock.internalFunction).toHaveBeenCalled();
  expect(result).toBe('mocked result');
});

These libraries provide a more type-safe and expressive way of mocking internal functions in TypeScript, making it easier to write and maintain your unit tests.