cache: move to backend package

internal/backend/cache/testing.go

@@ -0,0 +1,20 @@
+package cache
+
+import (
+	"testing"
+
+	"github.com/restic/restic/internal/restic"
+	"github.com/restic/restic/internal/test"
+)
+
+// TestNewCache returns a cache in a temporary directory which is removed when
+// cleanup is called.
+func TestNewCache(t testing.TB) *Cache {
+	dir := test.TempDir(t)
+	t.Logf("created new cache at %v", dir)
+	cache, err := New(restic.NewRandomID().String(), dir)
+	if err != nil {
+		t.Fatal(err)
+	}
+	return cache
+}