Implement resumable download queue (T-301)

core/downloader/files_test.go

@@ -0,0 +1,45 @@
+package downloader
+
+import (
+	"errors"
+	"os"
+	"testing"
+)
+
+func TestActivateCompletedRejectsReplacementOfWrittenPart(t *testing.T) {
+	paths, err := ensureTransferLayout(t.TempDir(), "request-identity")
+	if err != nil {
+		t.Fatalf("ensureTransferLayout() error = %v", err)
+	}
+	if err := os.WriteFile(paths.Part, []byte("trusted"), 0o600); err != nil {
+		t.Fatalf("WriteFile(original) error = %v", err)
+	}
+	original, expected, err := openVerifiedRegular(paths.Part, os.O_RDONLY)
+	if err != nil {
+		t.Fatalf("openVerifiedRegular() error = %v", err)
+	}
+	if err := original.Close(); err != nil {
+		t.Fatalf("Close(original) error = %v", err)
+	}
+	if err := os.Remove(paths.Part); err != nil {
+		t.Fatalf("Remove(original) error = %v", err)
+	}
+	if err := os.WriteFile(paths.Part, []byte("replacement"), 0o600); err != nil {
+		t.Fatalf("WriteFile(replacement) error = %v", err)
+	}
+
+	err = activateCompleted(paths, expected)
+	if !errors.Is(err, ErrTaskCorrupt) {
+		t.Fatalf("activateCompleted() error = %v, want %v", err, ErrTaskCorrupt)
+	}
+	if _, err := os.Stat(paths.Completed); !os.IsNotExist(err) {
+		t.Fatalf("completed path exists after identity mismatch: %v", err)
+	}
+	document, err := os.ReadFile(paths.Part)
+	if err != nil {
+		t.Fatalf("ReadFile(replacement) error = %v", err)
+	}
+	if string(document) != "replacement" {
+		t.Fatalf("replacement bytes = %q", document)
+	}
+}