Mock classes and interfaces, fully or partially in TypeScript

Question

What is the best way to mock classes and interfaces, fully or partially in TypeScript?

Jest is a popular test stack with mocking support, however according to this mocking single methods, classes and interfaces isn't supported in a fluent manner.

Answer 1

There are numerous mocking libraries specifically for TypeScript. Substitute.js is an excellent one. At the time of writing it addresses shortcomings in others, including:

• Fluent API. ts-mockito has a fluent API, however it is unable to mock interfaces. This is a show-stopper.
• Ability to create partial mocks.

It can also be fairly simply achieved with jest, as follows:

ClientDefaultImpl.prototype.authorize = jest.fn().mockImplementationOnce(
            () => Promise.resolve('xxx'));

Edit:

ts-mockito supports mocking of classes (and interfaces?) now.