test EventEmitter in the browser with Cypress

packages/web3-utils/test/integration/event_emitter.test.ts

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+/*
+This file is part of web3.js.
+
+web3.js is free software: you can redistribute it and/or modify
+it under the terms of the GNU Lesser General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+web3.js is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU Lesser General Public License for more details.
+
+You should have received a copy of the GNU Lesser General Public License
+along with web3.js.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+// this file contains the unit test for the event emitter in the DOM environment
+// it is executed in the jsdom environment (see "@jest-environment jsdom" in the top comment of this file)
+
+// ignore the following rule to allow keeping `@jest-environment jsdom` on top:
+// eslint-disable-next-line header/header
+import { EventEmitter } from '../../src/event_emitter';
+
+describe('EventEmitter in the browser with Cypress', () => {
+	let emitter: EventEmitter;
+
+	beforeEach(() => {
+		emitter = new EventEmitter();
+	});
+
+	describe('on', () => {
+		it('should add a listener for the specified event', () => {
+			const callback = jest.fn();
+			emitter.on('test', callback);
+			emitter.emit('test', 'hello');
+			expect(callback).toHaveBeenCalledWith('hello');
+		});
+	});
+
+	describe('once', () => {
+		it('should add a listener for the specified event that is only called once', () => {
+			const callback = jest.fn();
+			emitter.once('test', callback);
+			emitter.emit('test', 'hello');
+			emitter.emit('test', 'world');
+			expect(callback).toHaveBeenCalledTimes(1);
+			expect(callback).toHaveBeenCalledWith('hello');
+		});
+	});
+
+	describe('off', () => {
+		it('should remove a listener for the specified event', () => {
+			const callback = jest.fn();
+			emitter.on('test', callback);
+			emitter.off('test', callback);
+			emitter.emit('test', 'hello');
+			expect(callback).not.toHaveBeenCalled();
+		});
+	});
+
+	describe('emit', () => {
+		it('should call all listeners for the specified event', () => {
+			const callback1 = jest.fn();
+			const callback2 = jest.fn();
+			emitter.on('test', callback1);
+			emitter.on('test', callback2);
+			emitter.emit('test', 'hello');
+			expect(callback1).toHaveBeenCalledWith('hello');
+			expect(callback2).toHaveBeenCalledWith('hello');
+		});
+	});
+
+	describe('listenerCount', () => {
+		it('should return the number of listeners for the specified event', () => {
+			const callback1 = jest.fn();
+			const callback2 = jest.fn();
+			emitter.on('test', callback1);
+			emitter.on('test', callback2);
+			expect(emitter.listenerCount('test')).toBe(2);
+		});
+	});
+
+	describe('listeners', () => {
+		it('should return an array of listeners for the specified event', () => {
+			const callback1 = jest.fn();
+			const callback2 = jest.fn();
+			emitter.on('test', callback1);
+			emitter.on('test', callback2);
+			expect(emitter.listeners('test')).toEqual([callback1, callback2]);
+		});
+	});
+
+	describe('eventNames', () => {
+		it('should return an array of event names that have listeners', () => {
+			const callback1 = jest.fn();
+			const callback2 = jest.fn();
+			emitter.on('test1', callback1);
+			emitter.on('test2', callback2);
+			expect(emitter.eventNames()).toEqual(['test1', 'test2']);
+		});
+	});
+
+	describe('removeAllListeners', () => {
+		it('should remove all listeners for all events', () => {
+			const callback1 = jest.fn();
+			const callback2 = jest.fn();
+			emitter.on('test1', callback1);
+			emitter.on('test2', callback2);
+			emitter.removeAllListeners();
+			emitter.emit('test1', 'hello');
+			emitter.emit('test2', 'world');
+			expect(callback1).not.toHaveBeenCalled();
+			expect(callback2).not.toHaveBeenCalled();
+		});
+	});
+
+	describe('setMaxListeners', () => {
+		it('should set the maximum number of listeners for an event', () => {
+			emitter.setMaxListeners(2);
+			expect(emitter.getMaxListeners()).toBe(2);
+		});
+	});
+});