[Jest] Jest Typescript — mocking static method
Recently, I needed to mock a static method for my unit tests using Jest with Typescript. I’ve come across a few different ways to implement it, and this is my preferred way to do it.
Example Implementation
Given a class with a static method:
And the class under test that invokes the static method:
To mock the static method, simply assign jest.fn() to the static method like so:
Another scenario is when private constructor is used to instantiate a class (see: When to use a private constructor), the question arises — how do I mock the dependencies? Here’s how:
Given a dependency class that instantiate using a static get() method:
and the subject under test:
In the unit test, the dependency can be mocked in a similar fashion by mocking the static instantiation get() method and mock return the mock object:
and now the dependency can be mocked on spied on.
