feat: add unit tests and CI configuration

lib/utils/__tests__/logger.test.ts

@@ -0,0 +1,29 @@
+import { describe, it, expect, vi, beforeEach } from 'vitest'
+
+describe('logger', () => {
+  beforeEach(() => {
+    vi.resetModules()
+  })
+
+  it('calls console.error in development', async () => {
+    const spy = vi.spyOn(console, 'error').mockImplementation(() => {})
+    process.env.NODE_ENV = 'development'
+
+    const { logger } = await import('../logger')
+    logger.error('test error')
+
+    expect(spy).toHaveBeenCalledWith('test error')
+    spy.mockRestore()
+  })
+
+  it('calls console.warn in development', async () => {
+    const spy = vi.spyOn(console, 'warn').mockImplementation(() => {})
+    process.env.NODE_ENV = 'development'
+
+    const { logger } = await import('../logger')
+    logger.warn('test warning')
+
+    expect(spy).toHaveBeenCalledWith('test warning')
+    spy.mockRestore()
+  })
+})