GenericMockClass

GenericMockClass is a TypeScript class that provides a convenient way to create mock objects with spies and overrides for testing purposes. It is designed to be flexible and easy to use in various testing scenarios.

The GenericMockClass is designed to harness the capabilities of TypeScript generics, enabling autocomplete suggestions for methods and properties on the mock that mirror those available on the actual object.

Features

• Create mock objects with predefined overrides.
• Automatically generates spies for methods or properties.
• Easily override specific methods or properties.
• Mirror the interface of the actual object.

Installation

Install jest-generic-mock-class using npm:

npm install jest-generic-mock-class

Usage

Automatic spying on a method

interface ServiceToMock {
  methodToBeSpied: () => void;
}
const mock = GenericMockClass.create<ServiceToMock>();

// Call the method
mock.methodToBeSpied();

expect( mock.getSpyFor( 'methodToBeSpied' ) ).toHaveBeenCalled();

Automatic spying on a method with properties

interface ServiceToMock {
  methodToBeSpied: ( foo: string, bar: string ) => void;
}
const mock = GenericMockClass.create<ServiceToMock>();

// Call the method with arguments
mock.methodToBeSpied( 'foo', 'bar' );

expect( mock.getSpyFor( 'methodToBeSpied' ) ).toHaveBeenCalledWith( 'foo', 'bar' );
expect( mock.getSpyFor( 'methodToBeSpied' ) ).not.toHaveBeenCalledWith( 'baz' );

Returning a value from a method

interface ServiceToMock {
  methodToBeSpied: () => number;
}

const mock = GenericMockClass.create<ServiceToMock>( { methodToBeSpied: jest.fn().mockReturnValue( 123 ) } );
const returnValue = mock.methodToBeSpied();

expect( returnValue ).toBe( 123 );

Changing the return value of a method later

interface ServiceToMock {
  methodToBeSpied: () => number;
}

const mock = GenericMockClass.create<ServiceToMock>( { methodToBeSpied: jest.fn().mockReturnValue( 123 ) } );

// Change the return value
mock.override({ methodToBeSpied: jest.fn().mockReturnValue( 456 ) } );

// Call method
const returnValue = mock.methodToBeSpied();

expect( returnValue ).toBe( 456 );
expect( mock.getSpyFor( 'methodToBeSpied' ) ).toHaveBeenCalled();

Contributing

Contributions are welcome! If you find any issues or have suggestions for improvement, please open an issue or submit a pull request.