DEPRECATED: Yay! Jest has been rewritten in TypeScript, so you no longer need to use this library! Enjoy the beautiful types of Jest.

typeSafeJestSpy

A very thin layer that helps you write faster spies by automatically inferring the real implementation's type signature

Why would you use this?

• Have you ever made a spy for entirely the wrong function?
• Have you ever returned bad data from a spy by accident?
  • i.e. you knew that the method you were replacing was supposed to return a string... but you accidentally returned a number?

Who would want false-positive unit tests? Accidental mistakes with spies are a thing of the past with typeSafeJestSpy! :)

How do you use this?

• Please see the unit tests in the test folder for usage examples

Simply send your Jest spy into a function of this library and then the following Jest spy functions will require you to return the correct type:

• mockImplementation
• mockImplementationOnce
• mockResolvedValue
• mockResolvedValueOnce

Caveats

Please see the version of Jest in my package.json to see what this micro-library thinks is the way that Jest behaves. If your version of Jest is wildly different, then

• you might get irregular behavior.
• you might find that Jest has introduced a type-safe version itself, in which case this library would no longer be required