Test to detect new libraries added to the Dart SDK. (#1288)

test/tag/dart_sdk_libraries_test.dart

@@ -0,0 +1,45 @@
+// Copyright (c) 2023, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'dart:convert';
+import 'dart:io';
+
+import 'package:http/http.dart';
+import 'package:test/test.dart';
+
+/// This tests loads the library specification of the Dart SDK and tests if
+/// all of them are mentioned in `lib/src/tag/_specs.dart`.
+void main() {
+  test('Dart SDK libraries exist in _specs.dart', () async {
+    final rs = await get(Uri.parse(
+        'https://raw.githubusercontent.com/dart-lang/sdk/main/sdk/lib/libraries.json'));
+    expect(rs.statusCode, 200);
+    final parsed = json.decode(rs.body) as Map;
+    final allLibraries = <String>{};
+    for (final topLevel in parsed.entries) {
+      final tlv = topLevel.value;
+      if (tlv is! Map) {
+        continue;
+      }
+      final libraries = tlv['libraries'];
+      if (libraries is Map) {
+        allLibraries.addAll(libraries.keys.whereType<String>());
+      }
+    }
+    final publicLibraries =
+        allLibraries.where((e) => !e.startsWith('_')).toList();
+
+    final exempted = {
+      'vmservice',
+      'vmservice_io',
+    };
+    final specContent = await File('lib/src/tag/_specs.dart').readAsString();
+    for (final lib in publicLibraries) {
+      if (exempted.contains(lib)) {
+        continue;
+      }
+      expect(specContent, contains("'$lib'"));
+    }
+  });
+}