Jest Mock Date examples

Different approaches to mocking the Date in Jest tests

See the full post and explanation at codewithhugo.com/mocking-the-current-date-in-jest-tests.

There are 2 general approaches to mocking the current date:

• Using new Date() and mocking the constructor.
• Using new Date(Date.now()) and mocking the output of Date.now().

For each of those approaches in the application code, this repo has examples for a spy-based approach and a full function/constructor stub/mock replacement:

• Date.now() + full mock/stub: see ./src/stub-date-now.test.js
• Date.now() + spy: see ./src/spy-date-now.test.js
• new Date() + full mock/stub: see ./src/stub-date-class.test.js
• new Date() + spy: see ./src/spy-new-date.test.js

Running the tests

Packages were installed with yarn, although npm should work just as well.

• Run yarn
• Run yarn test