JS port of the C# AutoFixture library

Downloads in past


3232.0.0-03 years ago5 years agoMinified + gzip package size for @timreynolds/autofixture in KB


Build Status Maintainability
AutoFixture.js is based off of Mark Seeman's AutoFixture for .NET. The AutoFixture.js syntax attempts to match that of AutoFixture as much as possible where reasonable. You'll find the syntax and functionality applicable to JavaScript very similar and easy to understand.

Quick Start

npm install @timreynolds/autofixture

General Syntax

For the examples below, I'm going to assume that autofixture has already been require'd and assigned to the fixture variable.
The general syntax provided by AutoFixture.js follows:
const AutoFixture = require('@timreynolds/autofixture');
const fixture = new AutoFixture();
const instance = fixture.Create(ConstructorFunction[, args]);

What that means is that most of the constructor functions for the builtin JavaScript types are available.

String Creation

To create a string we'd do the following:
const myString = fixture.create(String);
// myString will look like a guid, e.g., '44CDC249-EAA2-4CC4-945C-B52475B0B0A9'

As with AutoFixture, we can also create a string that's prefixed by a value of our choosing. That's done by passing in a string:
const prefixedString = fixture.create("prefix");
// myString will look like a guid with our prefix. e.g.: 'prefix44CDC249-EAA2-4CC4-945C-B52475B0B0A9

Number Creation

To create a Number we'd do the following:
const myNumber = fixture.create(Number);
// myNumber will be a number between [0, 1). E.g., 0.59147235396

If we'd like a negative number or a larger number we can provide a multiplier:
const myNegativeNumber = fixture.create(Number, -1);
// myNegativeNumber will be between (-1, 0]. E.g., -0.7982537387376
const myLargeNumber = fixture.create(Number, 500);
// mylargeNumber will be between [0, 500). E.g., 423.8746491657
const myLargeNegativeNumber = fixture.create(Number, -700);
// myLargeNegativeNumber will be between (-700, 0]. E.g., -672.451987454916

Boolean Creation

To create a Boolean we can do the following:
const myBoolean = fixture.create(Boolean);
// myBoolean will be either true or false.

Object Creation

Creation From a Like Object

In JavaScript we frequently use objects and object literals and care not whether the object was created with a constructor function. AutoFixture.js handles this by using a provided object as a template, or specimen, for the object to be created.
To create an object that's similar to an existing object, just pass the object in to the create method:
const myObj = fixture.create({ prop1: "a string", prop2: 1.234, prop3: true });
myObj will look something like the following: 
  prop1: 'prop121032407-9216-404A-9F6A-021E8766AF21',
  prop2: 0.2518655981465,
  prop3: true

Each of the property values are randomly chosen from the set of allowable values. In the case of properties that are of type string the string value will be prefixed by the property name to allow the values to be easily distinguishable.

Building Objects

When writing tests cases you often need to exclude a property or set it to a predetermined value. This is achived by using the ObjectBuilder exposed in AutoFixture.js via build().
The builder provides the following methods;
  • like(template: {}): IObjectBuilder
  • without(propName: objectPath): IObjectBuilder
  • with(propName: objectPath, value: any): IObjectBuilder

const myObj = fixture
  .like({ prop1: "a string", prop2: 1.234, prop3: true })
  .with("prop4", "added property")
myObj will look something like the following: 
  prop2: 0.2518655981465,
  prop3: true,
  prop4: 'added property'

Object paths as supported by object-path can be used for with and without methods on the builder.

Creation From a Constructor Function

Just as the builtin constructor functions can be used to create strings, numbers, and booleans, custom constructor functions can be used to create other objects.
function MyObjectType() {
  this.prop1 = "";
  this.prop2 = "";
  this.prop3 = 0;
  this.prop4 = false;
const myObj = fixture.create(MyObjectType);
myObj will look something like the following:
  prop1: 'prop121032407-9216-404A-9F6A-021E8766AF21',
  prop2: 'prop27237F916-AAB4-40CF-814E-8BEC7181A70C',
  prop2: 0.98712634589712,
  prop3: true

As with Like-Object creation described above, the instance values are assigned based on their respective property types. Because prop and prop2 are strings, they were assigned random values prefixed by the property name.

Creating Many

When you're required to create an array the create method can be substituted for createMany.
This method takes an additional optional parameter for the number of items to be generated. By default his is set to a random number between 3 and 10.
const stringArray = fixture.createMany(String, 3);

Type Definitions

Due to the dynamic return types of the library only relativly basic type definitions are included. These will be improved overtime from real world usage.


This library is a TypeScript rewrite of NextITCorp/AutoFixture.js. Credit to them for the original work which wasn't published to NPM.