elmer-fudd

A test runner for smallish node projects with an opinionated take on mocking and very few dependencies. It helps you hunt for Bugs... get it?

|Package|Why| |:------|:--| |pirates| for patching require | |stack-trace| for identifying call sites |

Installation

$ npm install elmer-fudd

Minimal Example Project

package.json
src/
  multiply.js
  scale.js
test/
  multiply.test.js

{
  "elmer-fudd": {
    "ext": "test.js",
    "root": "test",
    "alias": {
      "@src": "src"
    }
  },
  "scripts": {
    "test": "elmer-fudd"
  },
}

const scale = require('./scale');
module.exports = (value) => value * scale;

module.exports = 10;

const { test, assert } = require('elmer-fudd');

test({
  name: 'Multiply without mocking',
  unit: '@src/multiply',
  spec: (multiply) => {
    assert.equal(multiply(5), 50);
  }
});

test({
  name: 'Multiply with mocked scale',
  unit: '@src/multiply',
  mock: [
    ['@src/scale', 2]
  ],
  spec: (multiply) => {
    assert.equal(multiply(5), 10);
  }
});

Testing Api

test

test takes a “test object” as an input, which allows you to specify a name, the unit you wish to test, any mocks you want to provide for dependencies, and a “spec” that runs assertions. Below are a few examples to get you started:

const { test, assert } = require('elmer-fudd');

test({
  name: 'Test with just a spec',
  spec: () => {
    assert.ok(true);
  }
});

const { test, assert } = require('elmer-fudd');

test({
  name: 'Unit testing a module',
  unit: './path/to/double.js'
  spec: (double) => {
    assert.equal(double(2), 4);
  }
});

const { test, assert } = require('elmer-fudd');

test({
  name: 'Unit testing a module',
  unit: './path/to/unit.js',
  mock: [
    ['.path', { fake: true }],
  ],
  spec: (double) => {
    assert.equal(double(2), 4);
  }
});

const { test, assert } = require('elmer-fudd');

test({
  name: 'Using a spec object',
  unit: './path/to/sum.js',
  spec: [
    { given: [1, 2], expect: 3 },
    { given: [1, 2, 3], expect: 6 },
  ]
});

assert

assert wraps node’s core assert.strict library so that failures can be grouped with tests. For detailed information see the docs. Here are a few examples to give you some ideas:

TODO examples that build...

mockFn

mockFn returns a mock function you can use in your specs. Here is how you might use a mock function.

const { mockFn } = require('elmer-fudd');

const fn = mockFn();

fn.returns(2);

fn(); // returns 2

It is not a comprehensive solution, but if you need something more robust there is no reason you cannot use something like sinon instead. Mock functions have the following methods and properties:

• fn.returns(value) makes the mock return a specific value
• fn.implementation(fn) adds an implementation to the mock
• fn.calledWith(...args) returns true if the mock has been called with these args
• fn.throws(err) when the mock is called, this error is thrown
• fn.resolves(value) the mock returns a promise that resolves this value
• fn.rejects(err) the mock returns a promise that rejects with this err
• fn.reset() resets the mock function
• fn.calls a getter that returns all the calls
• fn.count a getter that returns how many times the mock has been called

Tips & Tricks

Test driven?

You are allowed to mock the unit itself, which pared with "spec objects" creates a neat way you can write tests first without annoying failures. Then when you want to try the real unit you can comment out the test.

const { test, mockFn } = require('elmer-fudd')

test({
  name: 'test first?',
  unit: './my-busted-fn',
  mock: [
    ['./my-busted-fn', mockFn().will([
      { given: [2], output: 'foo' },
      { given: [2, { extra: true }], output: { bar: 2 } },
    ])]
  ],
  spec: [
    { given: [2], output: 'foo' },
    { given: [2, { extra: true }], output: { bar: 2 } }
  ],
})