jest-same-file-tests

This plugin helps with writing your Jest tests along side your code, which is common practice in Rust, and the community seams enamored with the approach.

Usage

Install jest-same-file-tests using yarn:

yarn add --dev jest-same-file-tests

Or npm:

npm install --save-dev jest-same-file-tests

Add the function as a global to the a jest setup file:

const tests = require('jest-same-file-tests').tests
global.tests = tests

TypeScript suport for injected global is in the TODO

Example

// file: example/src/mult.ts
export const mul = (a: number, b: number) => {
  return a * b;
};


tests('mul', () => {
  it('multiplies 2 x 3 = 6', () => {
    expect(mul(2, 3)).toEqual(6)
  })
})

// file: example/src/fact.ts
import { mul } from './mul'

export const fact = (_n: number) => {
  const n = Math.ceil(_n)
  if (n != _n) {
    throw Error("This function only supports integer values for n")
  }
  
  let result = 1
  for (let i = 2; i <= n; i ++) {
    result = mul(result, i)
  }

  return result
};

tests('fact', () => {
  it('calculates 4!', () => {
    expect(fact(4)).toEqual(1*2*3*4)
  })

  it('raises an error if a float is passed', () => {
    expect(() => fact(4.2)).toThrow(/This function only supports integer values/)
  })
})

If we didn't use the tests function and write describe blocks directly, when running a single file, the test runner would execute the tests for all the imported files. In the example above when running tests for fact the tests for mul would be run as well because fact imports mul.

TODOs

• Inject tests global type nicely for Typescript support
• Strip tests from build elegantly
• Figure out how to get Jest code coverage to work, currently files which tests are ignored.
• Figure out is there's a nicer way to work around the "Your test suite must contain at least one test". See comments in src/index.ts