test(e2e): add live DeepL compatibility test suite

Gated behind the e2e build tag so default go test and existing CI are unaffected. Covers free-endpoint translation, autodetection, input validation, and a paced no-429 upstream-compatibility canary, plus a scheduled/manual workflow.

.github/workflows/e2e.yaml

@@ -0,0 +1,23 @@
+name: E2E (DeepL compatibility)
+
+on:
+  workflow_dispatch:
+  schedule:
+    # Daily canary: catches the day DeepL changes its anti-bot scheme and
+    # DeepLX starts 429-ing, before users pile in with issues.
+    - cron: "17 2 * * *"
+
+permissions:
+  contents: read
+
+jobs:
+  e2e:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-go@v5
+        with:
+          go-version-file: go.mod
+          cache: true
+      - name: Run live DeepL E2E tests
+        run: go test -tags=e2e -v -timeout=10m ./translate/...

translate/translate_e2e_test.go

@@ -0,0 +1,151 @@
+//go:build e2e
+
+// End-to-end tests that exercise the real DeepL upstream through
+// TranslateByDeepLX. Gated behind the `e2e` build tag so the default
+// `go test ./...` (and existing CI) never hit the network or risk
+// tripping DeepL's rate limiting. Run explicitly:
+//
+//	go test -tags=e2e -v ./translate/...
+//
+// A 429 means THIS IP got rate-limited, not that the code is broken —
+// those cases back off and ultimately t.Skip rather than t.Fail, so the
+// suite stays a signal for "DeepLX can still reach DeepL", not a flaky
+// red build.
+package translate_test
+
+import (
+	"net/http"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/OwO-Network/DeepLX/translate"
+)
+
+const (
+	e2ePace       = 2 * time.Second
+	e2eBackoff    = 3 * time.Second
+	e2eMaxRetries = 3
+)
+
+// translateFree paces the call and backs off on 429. A persistent 429
+// skips the test (upstream/IP problem); anything else is returned to
+// assert on.
+func translateFree(t *testing.T, source, target, text string) translate.DeepLXTranslationResult {
+	t.Helper()
+	var res translate.DeepLXTranslationResult
+	for attempt := 1; attempt <= e2eMaxRetries; attempt++ {
+		time.Sleep(e2ePace)
+		var err error
+		res, err = translate.TranslateByDeepLX(source, target, text, "", "", "")
+		if err != nil {
+			t.Fatalf("TranslateByDeepLX returned a transport error: %v", err)
+		}
+		if res.Code == http.StatusTooManyRequests {
+			wait := time.Duration(attempt) * e2eBackoff
+			t.Logf("attempt %d/%d: DeepL returned 429 (this IP is rate-limited); backing off %s", attempt, e2eMaxRetries, wait)
+			time.Sleep(wait)
+			continue
+		}
+		return res
+	}
+	t.Skipf("DeepL kept returning 429 after %d attempts — upstream rate limit / IP block, not a code defect", e2eMaxRetries)
+	return res
+}
+
+func TestE2EFreeBasic(t *testing.T) {
+	res := translateFree(t, "EN", "ZH", "Hello, world")
+	if res.Code != http.StatusOK {
+		t.Fatalf("expected 200, got %d: %s", res.Code, res.Message)
+	}
+	if res.Data == "" {
+		t.Fatal("expected a non-empty translation, got empty Data")
+	}
+	if res.Method != "Free" {
+		t.Errorf("expected Method=Free, got %q", res.Method)
+	}
+	t.Logf("EN->ZH %q => %q", "Hello, world", res.Data)
+}
+
+func TestE2EFreeAutoDetect(t *testing.T) {
+	// Empty source => server-side language autodetection.
+	res := translateFree(t, "", "EN", "Bonjour le monde")
+	if res.Code != http.StatusOK {
+		t.Fatalf("expected 200, got %d: %s", res.Code, res.Message)
+	}
+	if res.Data == "" {
+		t.Fatal("expected a non-empty translation, got empty Data")
+	}
+	if res.SourceLang == "" {
+		t.Error("expected a detected SourceLang, got empty")
+	}
+	t.Logf("auto->EN %q => %q (detected %s)", "Bonjour le monde", res.Data, res.SourceLang)
+}
+
+func TestE2EFreeJapanese(t *testing.T) {
+	res := translateFree(t, "EN", "JA", "Good morning")
+	if res.Code != http.StatusOK {
+		t.Fatalf("expected 200, got %d: %s", res.Code, res.Message)
+	}
+	if res.Data == "" {
+		t.Fatal("expected a non-empty translation, got empty Data")
+	}
+}
+
+// TestE2ENoRateLimitOnNormalUse is the core of "make sure it doesn't 429":
+// a handful of properly-paced requests should essentially all succeed. If
+// every one is blocked we skip (IP problem); otherwise any 429 on paced
+// traffic means the browser impersonation is degrading and needs a look.
+func TestE2ENoRateLimitOnNormalUse(t *testing.T) {
+	phrases := []string{"one", "two", "three", "four", "five"}
+	var ok, rateLimited int
+	for i, p := range phrases {
+		time.Sleep(e2ePace)
+		res, err := translate.TranslateByDeepLX("EN", "ZH", p, "", "", "")
+		if err != nil {
+			t.Fatalf("round %d: unexpected transport error: %v", i, err)
+		}
+		switch res.Code {
+		case http.StatusOK:
+			ok++
+		case http.StatusTooManyRequests:
+			rateLimited++
+		default:
+			t.Errorf("round %d: unexpected code %d: %s", i, res.Code, res.Message)
+		}
+	}
+	t.Logf("normal-use rounds=%d ok=%d rateLimited=%d", len(phrases), ok, rateLimited)
+	if ok == 0 {
+		t.Skipf("all %d requests were rate-limited — upstream/IP block, not a code defect", len(phrases))
+	}
+	if rateLimited > 0 {
+		t.Errorf("got %d/%d 429s on properly-paced requests; DeepL impersonation may be degrading", rateLimited, len(phrases))
+	}
+}
+
+// TestE2EInputValidation never reaches the network — these inputs are
+// rejected before any DeepL call, so it is safe and free even under -tags=e2e.
+func TestE2EInputValidation(t *testing.T) {
+	cases := []struct {
+		name           string
+		source, target string
+		text           string
+		wantCode       int
+	}{
+		{"empty text", "EN", "ZH", "", http.StatusNotFound},
+		{"target auto", "EN", "auto", "hello", http.StatusBadRequest},
+		{"unsupported target", "EN", "XX", "hello", http.StatusBadRequest},
+		{"too long", "EN", "ZH", strings.Repeat("a", 1501), http.StatusRequestEntityTooLarge},
+	}
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			res, err := translate.TranslateByDeepLX(tc.source, tc.target, tc.text, "", "", "")
+			if err != nil {
+				t.Fatalf("unexpected error: %v", err)
+			}
+			if res.Code != tc.wantCode {
+				t.Errorf("want code %d, got %d: %s", tc.wantCode, res.Code, res.Message)
+			}
+		})
+	}
+}