jest / typescript / mock class prototype

README.md

What

You can use this helper to mock AND types your class methods.

Example

class A {
  foo(a: number, b: number): number { return a + b }
}

const a = mockClass(A.prototype)
a.foo.mockReturnValueOnce(32)

mockClass.helper.ts

export const mockClass = <T>(prototype: T) => {
  const descriptors = Object.getOwnPropertyDescriptors(prototype);
  const mockedVersion = Object.fromEntries(
    Object.entries(descriptors).map(([key, { value }]) => [key, typeof value === 'function' ? jest.fn() : value]),
  );

  return jest.mocked<T>(mockedVersion as T);
};