Testing HTTP Handlers – Table‑Driven Approach

Table‑Driven Handler Tests

This lesson explains the main concept clearly with beginner-friendly examples and background so you can learn why the code works.

func TestHandlers(t *testing.T) {
    tests := []struct {
        name       string
        method     string
        path       string
        body       string
        wantStatus int
        wantBody   string
    }{
        {"GET hello", http.MethodGet, "/hello", "", http.StatusOK, "Hello, World!\n"},
        {"POST echo", http.MethodPost, "/echo", "ping", http.StatusOK, "ping"},
    }

    // Setup router (could be chi, mux, etc.)
    r := http.NewServeMux()
    r.HandleFunc("/hello", helloHandler)
    r.HandleFunc("/echo", echoHandler)

    for _, tc := range tests {
        t.Run(tc.name, func(t *testing.T) {
            req := httptest.NewRequest(tc.method, tc.path, strings.NewReader(tc.body))
            w := httptest.NewRecorder()
            r.ServeHTTP(w, req)
            resp := w.Result()
            if resp.StatusCode != tc.wantStatus { t.Fatalf("status %d, want %d", resp.StatusCode, tc.wantStatus) }
            b, _ := io.ReadAll(resp.Body)
            if string(b) != tc.wantBody { t.Fatalf("body %q, want %q", b, tc.wantBody) }
        })
    }
}