jsmock

jsmock

Mocking framework for javascript, inspired by googlemock C++ framework. This project is still under construction ...

Installation

jsmock is published on npm

> npm install --save-dev jsmock

User Guide

Creating Mocks

const Mock = require('jsmock').Mock;

let foo = {
  bar: (a, b) => {
    return a + b
  }
};

let fooMock = new Mock(foo);

Now fooMock is a mock object wrapping foo. All functions of original object have been replaced and any call to foo.bar will cause an expection to be thrown.

expect(foo.bar.bind(foo)).to.throw(Error);

Defining Expectation

Expectation of function call is defined by calling expectCall on mock object.

fooMock.expectCall('bar');

By default this will setup an expectation of single call to foo.bar function with any arguments. As there is no action specified yet, nothing will be returned and no side effects will be observed.

Specifying Matcher

Matcher validates that call of mocked function is valid for given expectation. If no explicit matcher is specified expectation will be executed for any call to mocked function. Matcher can be specified as a predicate or simply as an arguments list to be verified against actual call.

fooMock.expectCall('bar', (a,b) => a > b);
foo.bar(3,2); // OK - 3 > 2
foo.bar(1,4); // KO - excpetion thrown

fooMock.expectCall('bar', 1, 8);
foo.bar(1, 8); // OK
foo.bar(1, 0); // KO 

Mathcher can be specified directly in arguments of the expectCall method or by calling matching function on mock object. Note that expectCall returns mock object making call chain possible:

fooMock.expectCall('bar').matching((a,b) => a < b);
fooMock.expectCall('bar').matching(1,4);

Specifying Actions

Action is an object encapsulating function to be executed instead of original code on mocked object. Besides a function each action specifies also number of times it's expected to be called. Each expectation can have multiple actions defined, which will be executed in order of creation.

fooMock.expectCall('bar')
  .willOnce((a,b) => a * b) // First call will return multiplication of arguments
  .will(6).times(3) // Next 3 calls will return value 6
  .willRepeteadly((a,b) => b) // All following calls will return second argument

You need to pay attention to order of specifying actions. If an action with unlimited number of expected calls preceeds other actions, it will prevent their execution and cause mock to be invalid.

Examples