ts-stubber

A generic stubbed instance creator to lazy stub any interface/class, while completely avoiding calling class's constructor. Thus, enabling both avoiding side effects that may occur while class constructor is activated and mocking Classes with no default constructor.

Documentation

Installation

npm i -D ts-stubber

or

yarn add -D ts-stubber

Usage

This library provides an API to create a stubbed instance of a class or interface, including property functions, allowing overrides of methods, setters and getters..

class MyClass {
  constructor(input: number) {
    throw new Error("Should not be called");
  }
  func(input: number, text: string) {
    console.log(text);
    return input;
  }
  property: number = 3;
  optionalProperty?: number;
  get getter(): number {
    return this.property;
  }
  set setter(value: number) {
    throw new Error("Should not be called");
  }
}

// creating a stubbed instance using the native node:test module
const const nodeStubbedInstanceCreator = StubbedInstanceCreator<MyClass, Mock<Function>>(
  () => mock.fn()
);

const nodeMockMyClass = nodeStubbedInstanceCreator.createStubbedInstance();

// creating a stubbed instance using sinon
const sinonStubbedInstanceCreator = StubbedInstanceCreator<MyClass, SinonStub>(
  () => sinon.stub()
);

const sinonMockMyClass = sinonStubbedInstanceCreator.createStubbedInstance();

// creating a stubbed instance using jest
const jestStubbedInstanceCreator = StubbedInstanceCreator<MyClass, jest.Mock>(
  () => jest.fn()
);

const jestMockMyClass = jestStubbedInstanceCreator.createStubbedInstance();

Caveats, Known Issues, and Limitations

Due to the lazy nature of the stubbing, for properties to exist in the stub, they must be overridden or set with a value.

class MyClass {
  property: number = 3;
  get getter(): number {
    return this.property;
  }
  set setter(value: number) {
    throw new Error("Should not be called");
  }
}

it("should have own property given property is overridden", () => {
  const mockMyClass = StubbedInstanceCreator<MyClass, jest.Mock>(() =>
    jest.fn()
  ).createStubbedInstance({ property: 5 }); // this test will fail if property is not overridden
  expect((<MyClass>mockMyClass).hasOwnProperty("property")).toBe(true);
});

it("should have own property given property is set", () => {
  const mockMyClass = StubbedInstanceCreator<MyClass, jest.Mock>(() =>
    jest.fn()
  ).createStubbedInstance();
  mockMyClass.property = 8; // this test will fail if property is not set
  expect((<MyClass>mockMyClass).hasOwnProperty("property")).toBe(true);
});

Testing

1. Set up the repo - yarn
2. Build the project - npm run build
3. Running Jest tests - npm run test
4. Running Cypress tests - npm run cy:run

License

This project is licensed under the MIT License - see the LICENSE.md file for details