adding ability to record logs for debug purposes

test/services/logger.test.js

@@ -0,0 +1,89 @@
+/*
+ * Copyright (c) 2026 by Christian Kellner.
+ * Licensed under Apache-2.0 with Commons Clause and Attribution/Naming Clause
+ */
+
+import { describe, it, expect, beforeEach, afterEach, vi } from 'vitest';
+import path from 'node:path';
+
+describe('services/logger.js - debug log sink', () => {
+  let logger;
+  let setDebugLogSink;
+  let consoleSpies;
+
+  beforeEach(async () => {
+    vi.resetModules();
+    const mod = await import(path.resolve('lib/services/logger.js'));
+    logger = mod.default;
+    setDebugLogSink = mod.setDebugLogSink;
+
+    // Silence console output so test runner stdout stays readable while still
+    // letting us inspect what the logger emitted if a test wants to.
+    consoleSpies = {
+      debug: vi.spyOn(console, 'debug').mockImplementation(() => {}),
+      info: vi.spyOn(console, 'info').mockImplementation(() => {}),
+      warn: vi.spyOn(console, 'warn').mockImplementation(() => {}),
+      error: vi.spyOn(console, 'error').mockImplementation(() => {}),
+    };
+  });
+
+  afterEach(() => {
+    setDebugLogSink(null);
+    for (const spy of Object.values(consoleSpies)) spy.mockRestore();
+  });
+
+  it('is a no-op for the sink when none is registered', () => {
+    // Just make sure nothing throws.
+    expect(() => logger.info('hello')).not.toThrow();
+    expect(() => logger.error(new Error('boom'))).not.toThrow();
+  });
+
+  it('forwards every log level (including debug) to the registered sink', () => {
+    const captured = [];
+    setDebugLogSink((entry) => captured.push(entry));
+
+    logger.debug('debug-line');
+    logger.info('info-line');
+    logger.warn('warn-line');
+    logger.error('error-line');
+
+    expect(captured).toHaveLength(4);
+    expect(captured.map((c) => c.level)).toEqual(['debug', 'info', 'warn', 'error']);
+    expect(captured[0].message).toContain('debug-line');
+    expect(captured[1].message).toContain('info-line');
+    expect(captured[2].message).toContain('warn-line');
+    expect(captured[3].message).toContain('error-line');
+    for (const c of captured) {
+      expect(typeof c.ts).toBe('number');
+    }
+  });
+
+  it('serializes Error stacks for the sink instead of "[object Object]"', () => {
+    const captured = [];
+    setDebugLogSink((entry) => captured.push(entry));
+
+    logger.error(new Error('boom'));
+
+    expect(captured).toHaveLength(1);
+    expect(captured[0].message).toContain('Error: boom');
+  });
+
+  it('stops forwarding once the sink is unregistered', () => {
+    const captured = [];
+    setDebugLogSink((entry) => captured.push(entry));
+    logger.info('one');
+    setDebugLogSink(null);
+    logger.info('two');
+
+    expect(captured).toHaveLength(1);
+    expect(captured[0].message).toContain('one');
+  });
+
+  it('does not break the caller when the sink throws', () => {
+    setDebugLogSink(() => {
+      throw new Error('sink exploded');
+    });
+    expect(() => logger.info('still works')).not.toThrow();
+    expect(consoleSpies.info).toHaveBeenCalled();
+  });
+});