implement MockLoggerService.ts testing utility

packages/backend/src/logger.ts

@@ -23,13 +23,16 @@ export type DataElement = DataObject | Error | string | null;
 // https://stackoverflow.com/questions/61148466/typescript-type-that-matches-any-object-but-not-arrays
 export type DataObject = Record<string, unknown> | (object & { length?: never; });
 
+export type Console = Pick<typeof global.console, 'error' | 'warn' | 'info' | 'log' | 'debug'>;
+export const nativeConsole: Console = global.console;
+
 const levelFuncs = {
 	error: 'error',
 	warning: 'warn',
 	success: 'info',
 	info: 'log',
 	debug: 'debug',
-} as const satisfies Record<Level, keyof typeof console>;
+} as const satisfies Record<Level, keyof Console>;
 
 // eslint-disable-next-line import/no-default-export
 export default class Logger {
@@ -37,12 +40,19 @@ export default class Logger {
 	private parentLogger: Logger | null = null;
 	public readonly verbose: boolean;
 
-	constructor(context: string, color?: KEYWORD, verbose?: boolean) {
+	/**
+	 * Where to send the actual log strings.
+	 * Defaults to the native global.console instance.
+	 */
+	private readonly console: Console;
+
+	constructor(context: string, color?: KEYWORD, verbose?: boolean, console?: Console) {
 		this.context = {
 			name: context,
 			color: color,
 		};
 		this.verbose = verbose ?? envOption.verbose;
+		this.console = console ?? nativeConsole;
 	}
 
 	@bindThis
@@ -94,7 +104,7 @@ export default class Logger {
 		} else if (data != null) {
 			args.push(data);
 		}
-		console[levelFuncs[level]](...args);
+		this.console[levelFuncs[level]](...args);
 	}
 
 	@bindThis

packages/backend/test/misc/MockLoggerService.ts

@@ -0,0 +1,74 @@
+/*
+ * SPDX-FileCopyrightText: hazelnoot and other Sharkey contributors
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import { jest } from '@jest/globals';
+import { Injectable } from '@nestjs/common';
+import type { KEYWORD } from 'color-convert/conversions.js';
+import type { Config } from '@/config.js';
+import Logger, { type Console } from '@/logger.js';
+import { LoggerService } from '@/core/LoggerService.js';
+import { bindThis } from '@/decorators.js';
+
+/**
+ * Mocked implementation of LoggerService.
+ * Suppresses all log output to prevent console spam, and records calls for assertions.
+ */
+@Injectable()
+export class MockLoggerService extends LoggerService {
+	/**
+	 * Mocked Console implementation.
+	 * All logs from all logger instances will be sent here.
+	 */
+	public readonly console: jest.Mocked<Console> = {
+		error: jest.fn(),
+		warn: jest.fn(),
+		info: jest.fn(),
+		log: jest.fn(),
+		debug: jest.fn(),
+	};
+
+	/**
+	 * Controls the verbose flag for logger instances.
+	 * Defaults to false (not verbose).
+	 */
+	public verbose: boolean;
+
+	constructor(config?: Config) {
+		config ??= { logging: { verbose: false } } as Config;
+		super(config);
+	}
+
+	/**
+	 * Resets the instance to initial state.
+	 * Mocks are reset, and verbose flag is cleared.
+	 */
+	@bindThis
+	public reset() {
+		this.console.error.mockReset();
+		this.console.warn.mockReset();
+		this.console.info.mockReset();
+		this.console.log.mockReset();
+		this.console.debug.mockReset();
+
+		this.verbose = false;
+	}
+
+	/**
+	 * Asserts that no errors and/or warnings have been logged.
+	 */
+	@bindThis
+	public assertNoErrors(opts?: { orWarnings?: boolean }): void {
+		expect(this.console.error).not.toHaveBeenCalled();
+
+		if (opts?.orWarnings) {
+			expect(this.console.warn).not.toHaveBeenCalled();
+		}
+	}
+
+	@bindThis
+	getLogger(domain: string, color?: KEYWORD | undefined): Logger {
+		return new Logger(domain, color, this.verbose, this.console);
+	}
+}