ez-mock

Simple mocking of require modules.

About

I found myself repeating a similar pattern for setting up mocks for unit tests. This package encapsulates that pattern and provides a simple, yet robust, interface.

Example

We want to test a simple module addToDBValue.js that adds an input value to a database value.

// addToDBValue.js
const queryDatabase = require('./database.js');
 
const addToDBValue = (inputValue) => {
  return inputValue + queryDatabase();
}
 
module.exports = addToDBValue;

The only issue is that database.js connects to an actual database.

// database.js
const queryDatabase = () => {
  /* database connection and query logic */
}
 
module.exports = queryDatabase;

But we don't want to touch any external systems for a unit test... We can simply mock that required dependency

// test.js
const {Mock, TestSubjectMocker} = require('ez-mock');
 
// database mock behavior that returns 1 from query
const databaseMockReturn1 = new Mock('./database.js', () => 1);
 
// database mock behavior that returns 2 from query
const databaseMockReturn2 = new Mock('./database.js', () => 2);
 
// set the default database mock to return 1 from query
const testSubjectMocker = new TestSubjectMocker('./addToDBValue.js', databaseMockReturn1);
 
// instantiate foo using the default database mock
let addToDBValue = testSubjectMocker.generateSubject();
console.log(addToDBValue(1)); // 2
console.log(addToDBValue(2)); // 3
 
// instantiate foo with an override mock behavior
addToDBValue = testSubjectMocker.generateSubject(databaseMockReturn2);
console.log(addToDBValue(1)); // 3
console.log(addToDBValue(2)); // 4

API

Mock(modulePath, functionality)

modulePath: String

The module name, absolute path, or relative path to the module you wish to mock.

functionality : object/function

The functionality you wish to return when require(...) is called.

TestSubjectMocker(modulePath, defaultMocks)

modulePath: String

The module name, absolute path, or relative path to the module you wish to test with its dependencies mocked.

defaultMocks : Mock/[Mock]

The mock behavior that will always be applied when generating a test subject.

TestSubjectMocker.generateTestSubject(overrideMocks)

defaultMocks : Mock/[Mock]

The mock behavior that overrides the default behavior for this instance of the test subject.

returns : object/function

An instance of the test subject with the mocks applied

TestSubjectMocker.clearMocks()

Clears all registered mocks (even the default mocks)