Add test for soong/testing/test_spec.

This CL adds test for test_spec.go and all_test_specs.go (singleton).

Bug: 296873595
Test: m nothing --no-skip-soong-tests -j96

Change-Id: I5010c68512e75d1b9a337c02da86faac15e376fe

testing/test.go

@@ -0,0 +1,21 @@
+// Copyright 2023 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package testing
+
+import (
+	"android/soong/android"
+)
+
+var PrepareForTestWithTestSpecBuildComponents = android.FixtureRegisterWithContext(RegisterBuildComponents)