babel-plugin-arrow-test

Babel 6 plugin, allows you to test anonymous javascript arrow functions easily.

The problem

I love to write declarative javascript code like

blabla
  .map(({ x, y }) => ({z: x + y}))
  .reduce((memo, { z }) =>  ... )
  .filter(({ ... }) => ... )
  .groupBy( ... )

Writing full test of this flow can be not an easy task for real flows with many map, reduce and other functions we like. But almost every function inside flow is easily testable.

But even if any of arrow function in this flow is easily testable, to test each I need to write something like this.

// now I can import mappingFunction and test
export const mapFn = ({ x, y }) => ({z: x + y});
export const reduceFn = (memo, { z }) =>  ... ;
...

blabla
  .map(mappingFunction)
  .reduce(reduceFunction)
  ...

This can easily be tested, but source is unreadable. Function definition is far outside from place I use it.

So this plugin allows you to solve this problem.

Solution

Just add comment to each anonymous function you want to test

// file.js
blabla
  .map( /* @t(mapFn) */ ({ x, y }) => ({z: x + y}))
  .reduce(
    // @t(reduceFn)
    (memo, { z }) =>  ...
  )
  ...

Add next lines to .babelrc

"env": {
  "ARROW": {
    "plugins": [
      ["arrow-test", {"regexp": "@t\\(([^\\)]+)\\)"}]
    ]
  }
}

Write test

// test anonymous mapFn reduceFn
describe('must import anonymouse functions', () => {
  it('must import anonymouse functions', () => {
    const { mapFn, reduceFn } = require('./file.js');
    expect(mapFn({ x: 1, y: 2 })).toEqual({ z: 3});
  });
}

And run with

NODE_ENV=ARROW mocha

All anonymous functions with comment you describe as plugin regexp parameter will be exported with regexp capture so you can test them

Examples

map reduce

Simple map reduce module and test

recompose

Functional react component with recompose and test

Install

npm install --save-dev babel-plugin-arrow-test

Add to .babelrc

"env": {
  "ARROW": {
    "plugins": [
      ["arrow-test", {"regexp": "@t\\(([^\\)]+)\\)"}]
    ]
  }
}