jest-typed-mock

Make unit tests great again!

jest-typed-mock brings type checking to the wild __mocks__ of Jest. Helping you maintain the correct mocks, matching the real files, they are going to mock. This is like eslint, but for mocks.
` Manual mocks are defined by writing a module in a __mocks__/ subdirectory immediately adjacent to the module. For example, to mock a module called user in the models directory, create a file called user.js and put it in the models/__mocks__ directory. ` https://facebook.github.io/jest/docs/en/manual-mocks.html#content Add to your package.json ```json "scripts": {

...
"jest-typed-mock": "jest-typed-mock flow",       // for Flow 
"jest-typed-mock": "jest-typed-mock typescript", // for TS
"jest-typed-mock": "jest-typed-mock javascript", // for JS
"jest-typed-mock": "jest-typed-mock exports",    // only check names
...

} ``` In some cases (always?) you have to specify babel env.Rewiremock can provide a type safety to dependency mocking, but Jest do had it's own mocking (and sandboxing) system. As long rewiremock still able to work, even under the Jest management - it is now a quite good idea.
jest-typed-mock is not a library. It is just a small tool, which can check mocked file against the real one.
Lets imagine - we have a.js

//a.js
export const function1 = (a:number):number => a**2;
export const function2 = (a:number):number => a*2;
export default (a:string) => a.substr(1)

and __mocks__/a.js

export const function1 = (a:number):number => 1;
export const function2 = (a:number):number => 2;
export default (a:string) => "3"

It is ok. But next you change the real a.js

//a.js
// function 1 is changed
export const function1 = (a:string):number => parseInt(a);
// function 2 is removed
export default (a:string) => a.substr(1)

But your tests are still using the old __mocks__, and they are still green.
jest-typed-mock just matches real files and mocks.

TS:

`` Property 'function2' is missing in type 'typeof "....a"'. ``

Flow:

`property function2 of exports of "/__mocks__/a.js". Property not found in const real = () => import('/a.js');`

JS

As long there is no types, could only test exported names as their types(object, number, function), and function arguments count. Even this is quite helpful. `jest-typed-mock: mocked export "function2" does not exists in a.js` jest-typed-mock will also try to check function agains function, at least argument count, which can break a lot of things. To bypass this checking use `jest-typed-mock exports`, or specify noFunctionCompare in API options ```js require('jest-typed-mock/runjs')(dirname , {noFunctionCompare: true}) ```

Result

As result - you reduce a smell of mocking. Mocks becomes less fake, and tests becomes less flake.

Licence

MIT