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?

Dependencies

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

package.json

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

src/multiply.js

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

src/scale.js

module.exports = 10;

test/multiply.test.js

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:

Test with just a spec

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

Unit testing a module

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

Unit testing a module with mocked dependencies

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);
  }
});

Unit testing a module with a spec object

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 } }
  ],
})