Add the tests of the spec generator to the unit tests

pkg/analyzer_plugin/tool/spec/check_all_test.dart

Index: pkg/analyzer_plugin/tool/spec/check_all_test.dart
diff --git a/pkg/analyzer_plugin/tool/spec/check_all_test.dart b/pkg/analyzer_plugin/tool/spec/check_all_test.dart
index 3625eb59c0e6bde210e5e8a16ea632cd6b584062..db9d2e5a3e2bce43617ddeb7f4536a84134a37af 100644
--- a/pkg/analyzer_plugin/tool/spec/check_all_test.dart
+++ b/pkg/analyzer_plugin/tool/spec/check_all_test.dart
@@ -15,6 +15,9 @@ import 'generate_all.dart';
  */
 main() {
   String script = Platform.script.toFilePath(windows: Platform.isWindows);
-  String pkgPath = normalize(join(dirname(script), '..', '..'));
-  GeneratedContent.checkAll(pkgPath, 'tool/spec/generate_all.dart', allTargets);
+  List<String> components = split(script);
+  int index = components.indexOf('analyzer_plugin');
+  String pkgPath = joinAll(components.sublist(0, index + 1));
+  GeneratedContent.checkAll(
+      pkgPath, join('tool', 'spec', 'generate_all.dart'), allTargets);
 }