diff --git a/test/lib/sunpump.test.ts b/test/lib/sunpump.test.ts
new file mode 100644
index 0000000..183e783
--- /dev/null
+++ b/test/lib/sunpump.test.ts
@@ -0,0 +1,34 @@
+import { SunPump, SunPumpHttpError, SUNPUMP_DEFAULT_BASE_URL } from '../../src/lib/sunpump'
+
+describe('SunPump', () => {
+  it('uses default base URL', () => {
+    const client = new SunPump()
+    expect(SUNPUMP_DEFAULT_BASE_URL).toBe('https://api-v2.sunpump.meme/pump-api')
+  })
+
+  it('accepts custom base URL', () => {
+    const client = new SunPump({ baseUrl: 'https://custom.example.com/api' })
+    expect(client).toBeDefined()
+  })
+
+  it('accepts custom fetch implementation', () => {
+    const mockFetch = jest.fn()
+    const client = new SunPump({ fetchImpl: mockFetch as unknown as typeof fetch })
+    expect(client).toBeDefined()
+  })
+})
+
+describe('SunPumpHttpError', () => {
+  it('has correct error code', () => {
+    const err = new SunPumpHttpError('test error', 404, 'not found')
+    expect(err.code).toBe('SUNPUMP_HTTP_ERROR')
+    expect(err.status).toBe(404)
+    expect(err.body).toBe('not found')
+    expect(err.message).toBe('test error')
+  })
+
+  it('is an instance of Error', () => {
+    const err = new SunPumpHttpError('test', 500)
+    expect(err).toBeInstanceOf(Error)
+  })
+})