feat(exp): add mock utils package (#460)

Test helper to mock http request made with the hcloud-go library.

hcloud/exp/mockutils/mockutils.go

@@ -0,0 +1,72 @@
+package mockutils
+
+import (
+	"encoding/json"
+	"net/http"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+// Request describes a http request that a [httptest.Server] should receive, and the
+// corresponding response to return.
+//
+// Additional checks on the request (e.g. request body) may be added using the
+// [Request.Want] function.
+//
+// The response body is populated from either a JSON struct, or a JSON string.
+type Request struct {
+	Method string
+	Path   string
+	Want   func(t *testing.T, r *http.Request)
+
+	Status  int
+	JSON    any
+	JSONRaw string
+}
+
+// Handler is used with a [httptest.Server] to mock http requests provided by the user.
+//
+// Request matching is based on the request count, and the user provided request will be
+// iterated over.
+func Handler(t *testing.T, requests []Request) http.HandlerFunc {
+	t.Helper()
+
+	index := 0
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if testing.Verbose() {
+			t.Logf("call %d: %s %s\n", index, r.Method, r.RequestURI)
+		}
+
+		if index >= len(requests) {
+			t.Fatalf("received unknown call %d", index)
+		}
+
+		expected := requests[index]
+		require.Equal(t,
+			expected.Method+" "+expected.Path,
+			r.Method+" "+r.RequestURI,
+		)
+
+		if expected.Want != nil {
+			expected.Want(t, r)
+		}
+
+		w.WriteHeader(expected.Status)
+		switch {
+		case expected.JSON != nil:
+			w.Header().Set("Content-Type", "application/json")
+			if err := json.NewEncoder(w).Encode(expected.JSON); err != nil {
+				t.Fatal(err)
+			}
+		case expected.JSONRaw != "":
+			w.Header().Set("Content-Type", "application/json")
+			_, err := w.Write([]byte(expected.JSONRaw))
+			if err != nil {
+				t.Fatal(err)
+			}
+		}
+
+		index++
+	})
+}

hcloud/exp/mockutils/mockutils_test.go

@@ -0,0 +1,53 @@
+package mockutils
+
+import (
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestHandler(t *testing.T) {
+	server := httptest.NewServer(Handler(t, []Request{
+		{
+			Method: "GET", Path: "/",
+			Status: 200,
+			JSON: struct {
+				Data string `json:"data"`
+			}{
+				Data: "Hello",
+			},
+		},
+		{
+			Method: "GET", Path: "/",
+			Status:  400,
+			JSONRaw: `{"error": "failed"}`,
+		},
+	}))
+	defer server.Close()
+
+	// Request 1
+	resp, err := http.Get(server.URL)
+	require.NoError(t, err)
+	assert.Equal(t, 200, resp.StatusCode)
+	assert.Equal(t, `{"data":"Hello"}`, readBody(t, resp))
+
+	// Request 2
+	resp, err = http.Get(server.URL)
+	require.NoError(t, err)
+	assert.Equal(t, 400, resp.StatusCode)
+	assert.Equal(t, `{"error": "failed"}`, readBody(t, resp))
+}
+
+func readBody(t *testing.T, resp *http.Response) string {
+	t.Helper()
+
+	body, err := io.ReadAll(resp.Body)
+	require.NoError(t, err)
+	require.NoError(t, resp.Body.Close())
+	return strings.TrimSuffix(string(body), "\n")
+}