Fluent pluggable interface for easily wrapping describe, it, and test blocks in Jest tests.

var wrap = require('jest-wrap');
var expect = require('chai').expect;

var mockWindow = {
	location: {
		href: 'test/url'
	}
};
wrap().withGlobal('window', () => mockWindow).describe('mocked window', function () {
	it('is mocked', function () {
		expect(window).to.equal(mockWindow);
	});

	it('has the right URL', function () {
		expect(window.location.href).to.equal('test/url');
	});
});

var obj = { a: 1 };
wrap().withOverrides(() => obj, () => ({ a: 2, b: 3 })).describe('overridden object keys', function () {
	it('has "b"', function () {
		expect(obj.b).to.equal(3);
	});

	it('has overridden "a"', function () {
		expect(obj.a).to.equal(2);
	});
});

wrap().withOverride(() => obj, 'a', () => 4).skip().describe('this test is skipped', function () {
	it('also supports .only()!', function () {
		expect(true).to.equal(false); // skipped
	});
});

A jest-wrap plugin is a named function that returns a JestWrapper instance or a descriptor object.

• A plugin’s function name must begin with the string “with”.

• Plugins can be globally registered, or .used ad-hoc.

• .use requires a plugin function as its first argument; further arguments are passed through to the plugin.

• .extend requires a non-empty description string, and a descriptor object which may contain a value that is a function, or an array of functions, whose keys correspond to any or all of the supported jest methods.

• Globally registered plugins, .use calls, and .extend calls can be chained, stored, and reused - each link in the chain creates a new instance of a JestWrapper.

• A descriptor object may contain any or all of these 5 keys:

• a description string, for use in “describe” and/or “it” (this is required when returning an object)

• beforeEach: a function, or array of functions, for use in a jest beforeEach function

• afterEach: a function, or array of functions, for use in a jest afterEach function

• beforeAll: a function, or array of functions, for use in a jest beforeAll function

• afterAll: a function, or array of functions, for use in a jest afterAll function

The most common approach will be for a plugin function to return this.extend(description, descriptor).

A plugin function must have a name that starts with “with”, and will be invoked with a receiver (”this” value) of a JestWrapper instance.

To register a plugin, call the register function on jest-wrap with the plugin function. This should not be done in a reusable module.

module.exports = function withFoo(any, args, you, want) {
	return this.extend('with some foo stuff', {
		beforeEach: function () {
			// setup ran before each test
		},
		afterEach: [
			function () {
				// teardown ran after each test
			},
			function () {
				// more teardown
			}
		],
		beforeAll: function () {
			// setup ran once before all tests
		},
		afterAll: function () {
			// teardown ran once after all tests
		}
	});
};

var wrap = require('jest-wrap');
wrap.register(require('jest-wrap-with-foo'));

wrap().withFoo().describe…

Although jest has describe.skip, describe.only, it.skip, it.only, test.skip, and test.only, it is not possible to implement these in jest-wrap without using ES5 property accessors. Since this project supports ES3, we decided to use .skip().describe etc rather than forfeit the ability to have skip/only.

Simply clone the repo, npm install, and run npm test