Test HTTP handlers

Test HTTP handlers by using httptest.NewRecorder and httptest.NewRequest to simulate requests and verify responses.

Use httptest.NewRecorder to capture the response and httptest.NewRequest to simulate the request, then assert the status code and body.

func TestHandler(t *testing.T) {
    req := httptest.NewRequest("GET", "/", nil)
    w := httptest.NewRecorder()
    handler(w, req)
    if w.Code != http.StatusOK {
        t.Errorf("handler returned wrong status code: got %v want %v", w.Code, http.StatusOK)
    }
}