Fabricator

Fabricate objects for your tests

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The Problem

Fabricator is based on the excellent Fabrication. Its purpose is to easily generate objects in JavaScript. It is particularly useful for testing.

Installation

npm install --dev @mosattler/fabricator

Defining Models

Models are defined with Fabricator() in this way:

import { Fabricator } from "@mosattler/fabricator";
import faker from "faker";
import { uniqueId } from "lodash";

interface User {
  id: number;
  name: string;
  admin: false;
}

const userFabricator = Fabricator<User>({
  id: () => uniqueId(),
  name: () => faker.name.firstName() + faker.name.lastName(),
  admin: false,
});

You simply pass a model definition. The definition is an object where each key is a function. If you need dynamic data you can use a library like faker.

You can also extend existing models. For example:

interface Admin extends User {
  admin: true;
}

const adminFabricator = userFabricator.extend<Admin>({ admin: true });

In this case, adminFabricator will inherit all the properties from userFabricator but will overwrite the value for the admin property.

Fabricating Objects

Once your model is defined you can create it by calling the returned function:

const user = userFabricator();
// => { id: 1, name: 'John Doe', admin: false }
const admin = adminFabricator();
// => { id: 2, name: 'Susan Smith', admin: true }

You can overwrite some values by passing a model definition as parameter:

const blockedUser = userFabricator({ isBlocked: true });
// => { id: 3, name: 'Donald Brown', admin: false, isBlocked: true }

Note that there's a difference between passing a function and a static value in a fabricator definition. A function gets executed every time you create a new object, a constant value is cached. Consider the following example:

const withConstant = Fabricator({ foo: Math.random() });
withConstant(); // => { foo: 0.11134742452557367 }
withConstant(); // => { foo: 0.11134742452557367 }
withConstant(); // => { foo: 0.11134742452557367 }

const withMethod = Fabricator({ foo: () => Math.random() });
withMethod("withMethod"); // => { foo: 0.4426388385403983 }
withMethod("withMethod"); // => { foo: 0.572825488636862 }
withMethod("withMethod"); // => { foo: 0.4322506522885017 }