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moq.ts | documentation

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moq.ts | Documentation

Moq for Typescript. Inspired by c# Moq library.


This implementation depends on Proxy object. So if your production code is not compatible with this I would recommend you separate you production code and testing code into dedicated projects. If you need help with this then ask me.


npm install moq.ts --save-dev

Quick start

moq.ts as the original Moq library is intended to be simple to use, strongly typed (no magic strings!, and therefore full compiler-verified and refactoring-friendly) and minimalistic (while still fully functional!).

You can find a pretty full set of usages in the integration tests. Check out tests.integration folder.

Mocking property of objects - mock-get.property.spec.ts

import {Mock, It, Times, ExpectedGetPropertyExpression} from 'moq.ts';
interface ITestObject {
    property1: number;
    property2: number;
    property3: number;
    property4: number;
    method(): void;

const property4Name = 'property4';
const mockName = 'mock name is optional';
const mock = new Mock<ITestObject>(mockName)
    .setup(instance => instance.property1)

    .setup(instance => It.Is((expression: ExpectedGetPropertyExpression) => expression.name === 'property2'))

    //let's deny any write operation on the property for all values
    .setup(instance => {instance.property2 = It.Is(() => true)})

    .setup(instance => instance.property3)
    .callback(()=> 10 + 10)

    .setup(instance => instance[property4Name])
    .throws(new Error('property4 access'))

    //since a method is a property that holds a pointer to a function
    .setup(instance => instance.method)
    .returns(()=>{console.log('The method was called')});

const object = mock.object();

mock.verify(instance=> instance.property1, Times.Never());

Mocking property setting - The documentation on returned value from 'set hook' on Proxy object


import {Mock, It, Times, ExpectedSetPropertyExpression} from 'moq.ts';
interface ITestObject {
    property: number|any;

const value = {field: new Date()};

const mock = new Mock<ITestObject>()
    .setup(instance => {instance.property = 1})
    //true - allows the write operation

    .setup(instance => It.Is((expression: ExpectedSetPropertyExpression) => expression.name === 'property' && expression.value === 2))
    //false - denies the write operation

    .setup(instance => {instance.property = It.Is(value => value === 3)})
    // allows the write operation
    .callback(()=> true)

    .setup(instance => {instance.property = value})
    .throws(new Error('an object has been written into property'));

const object = mock.object();
object.property = 1;

mock.verify(instance=> {instance.property = 1}, Times.Once());

Mocking functions -


import {Mock, It, Times} from 'moq.ts';
interface ITestFunction {
    (arg: number|any): string;

const value = {field: new Date()};

const mock = new Mock<ITestFunction>()
    .setup(instance => instance(1))
    .returns('called with 1')

    .setup(instance => instance(2))
    .callback((argument)=> argument === 2 ? 'called with 2' : `called with ${argument}`)

    .setup(instance => instance(value))
    .throws(new Error('Argument is object with date'))

    .setup(instance => instance(It.Is(value => value === 4)))
    .returns('called with 4');

const method = mock.object();
const actual = method(1);

mock.verify(instance => instance(1), Times.Once());
mock.verify(instance => instance(It.Is(value=> value === 1)), Times.Exactly(1));

Mocking functions of objects - mock-named.method.spec.ts

import {Mock, It, Times} from 'moq.ts';
interface ITestObject {
    method(arg1: number, arg2: string): Date;

const values = ['a', 'b', 'c'];

const mock = new Mock<ITestObject>()
    .setup(instance => instance.method(1, values[0]))
    .returns(new Date(2016))

    .setup(instance => instance.method(It.Is(value => value === 2), values[1]))
    .callback((arg1, arg2)=> new Date(2017 + arg1))

    .setup(instance => instance.method(3, It.Is(value => value === values[2])))
    .throws(new Error('Invoking method with 3 and c'));

const object = mock.object();
const actual = object.method(1, 'a');

mock.verify(instance => instance.method(2, 'a'), Times.Never());

Mock behavior

A mocked object is a Proxy, that configured to track any read and write operations on properties. If you write a value to an arbitrary property the mocked object will keep it and you can read it later on. By default the prototype of mocked object is Function.

Accessing to an unset property or a method will return undefined or a pointer to a spy function if it exists on prototype; You can call this function and it will be tracked.

The default behaviour has the lowest precedence. The latest setup has the highest precedence.

You can control mock behavior when accessing to a property without a corresponding setup.

    mock = new Mock<ITestObject>();
    mock.setup(instance => It.Is(expression => true))
      .throws(new Error("setup is missed"));

The behaviour API is obsolete. In future versions it will behave as its prototype which is Object by default and desired behaviours should be set thought custom setups.

    mock = new Mock<ITestObject>()
    .setBehaviorStrategy(MockBehavior.Loose) //obsolete
    .setBehaviorStrategy(MockBehavior.Strict); //obsolete

The default behavior is strict.

Mock prototype

If you need to make work instanceof operator or you need to deal with prototype of the mock object you can use prototypeof function of Mock class. Or you can use Object.getPrototypeOf or Object.setPrototypeOf functions on mocked object.

class TestObject implements ITestObject {


const mock = new Mock<ITestObject>()

mock.object() instanceof TestObject;// true


If you need to replicate behaviour of an existing object you can reflect mock's interactions on the object.

class Origin {
    public property = 0;

    public method(input: number): number {
        return input * this.property;

const origin = new Origin();

const mock = new Mock<Origin>()
    .setup(() => It.IsAny())

const mocked = mock.object();
mocked.property = 3;
const actual = mocked.method(2);

mock.verify(instance => instance.method(2));

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