first commit

packages/nodes-base/nodes/MQTT/test/GenericFunctions.test.ts

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+import { mock } from 'jest-mock-extended';
+import { MqttClient } from 'mqtt';
+import { ApplicationError } from '@n8n/errors';
+
+import { createClient, type MqttCredential } from '../GenericFunctions';
+
+describe('createClient', () => {
+	beforeEach(() => jest.clearAllMocks());
+
+	it('should create a client with minimal credentials', async () => {
+		const mockConnect = jest.spyOn(MqttClient.prototype, 'connect').mockImplementation(function (
+			this: MqttClient,
+		) {
+			setImmediate(() => this.emit('connect', mock()));
+			return this;
+		});
+
+		const credentials = mock<MqttCredential>({
+			protocol: 'mqtt',
+			host: 'localhost',
+			port: 1883,
+			clean: true,
+			clientId: 'testClient',
+			ssl: false,
+		});
+		const client = await createClient(credentials);
+
+		expect(mockConnect).toBeCalledTimes(1);
+		expect(client).toBeDefined();
+		expect(client).toBeInstanceOf(MqttClient);
+		expect(client.options).toMatchObject({
+			protocol: 'mqtt',
+			host: 'localhost',
+			port: 1883,
+			clean: true,
+			clientId: 'testClient',
+		});
+	});
+
+	it('should reject with ApplicationError on connection error and close connection', async () => {
+		const mockConnect = jest.spyOn(MqttClient.prototype, 'connect').mockImplementation(function (
+			this: MqttClient,
+		) {
+			setImmediate(() => this.emit('error', new Error('Connection failed')));
+			return this;
+		});
+		const mockEnd = jest.spyOn(MqttClient.prototype, 'end').mockImplementation();
+
+		const credentials: MqttCredential = {
+			protocol: 'mqtt',
+			host: 'localhost',
+			port: 1883,
+			clean: true,
+			clientId: 'testClientId',
+			username: 'testUser',
+			password: 'testPass',
+			ssl: false,
+		};
+
+		const clientPromise = createClient(credentials);
+
+		await expect(clientPromise).rejects.toThrow(ApplicationError);
+		expect(mockConnect).toBeCalledTimes(1);
+		expect(mockEnd).toBeCalledTimes(1);
+	});
+});