Make sure to finish the suite if all tests are skipped (flutter/engine#49339)

Fixes https://github.com/flutter/flutter/issues/140481

Before this fix, if all tests are skipped, the `onDone` callback never fires, which means the recieve port never closes, which means the process just hangs indefinitely (and the success message is never printed).

engine/src/flutter/testing/litetest/lib/src/test_suite.dart

@@ -40,12 +40,22 @@ class TestSuite {
       );
     }
     if (skip) {
-      _logger.writeln('Test $name: Skipped');
+      _logger.writeln('Test "$name": Skipped');
+      _primeQueue();
       return;
     }
     _pushTest(name, body);
   }
 
+  void _primeQueue() {
+    if (!_testQueuePrimed) {
+      // All tests() must be added synchronously with main, so we can enqueue an
+      // event to start all tests to run after main() is done.
+      Timer.run(_startAllTests);
+      _testQueuePrimed = true;
+    }
+  }
+
   void _pushTest(
     String name,
     dynamic Function() body,
@@ -53,12 +63,7 @@ class TestSuite {
     final Test newTest = Test(name, body, logger: _logger);
     _testQueue.add(newTest);
     newTest.state = TestState.queued;
-    if (!_testQueuePrimed) {
-      // All tests() must be added synchronously with main, so we can enqueue an
-      // event to start all tests to run after main() is done.
-      Timer.run(_startAllTests);
-      _testQueuePrimed = true;
-    }
+    _primeQueue();
   }
 
   void _startAllTests() {
@@ -72,6 +77,10 @@ class TestSuite {
       });
     }
     _lifecycle.onStart();
+    if (_testQueue.isEmpty) {
+      _logger.writeln('All tests skipped.');
+      _lifecycle.onDone(_testQueue);
+    }
   }
 }
 

engine/src/flutter/testing/litetest/test/litetest_test.dart

@@ -4,6 +4,7 @@
 
 import 'dart:async';
 import 'dart:collection';
+import 'dart:isolate';
 
 import 'package:async_helper/async_helper.dart';
 import 'package:async_helper/async_minitest.dart';
@@ -13,6 +14,25 @@ import 'package:litetest/src/test_suite.dart';
 Future<void> main() async {
   asyncStart();
 
+  test('skip', () async {
+    final StringBuffer buffer = StringBuffer();
+    final TestLifecycle lifecycle = TestLifecycle();
+    final TestSuite ts = TestSuite(
+      logger: buffer,
+      lifecycle: lifecycle,
+    );
+
+    ts.test('Test', () {
+      expect(1, equals(1));
+    }, skip: true);
+    final bool result = await lifecycle.result;
+
+    expect(result, true);
+    expect(buffer.toString(), equals(
+      'Test "Test": Skipped\nAll tests skipped.\n',
+    ));
+  });
+
   test('test', () async {
     final StringBuffer buffer = StringBuffer();
     final TestLifecycle lifecycle = TestLifecycle();
@@ -211,6 +231,8 @@ Test "Test3": Passed
 }
 
 class TestLifecycle implements Lifecycle {
+  final ReceivePort port = ReceivePort();
+
   final Completer<bool> _testCompleter = Completer<bool>();
 
   Future<bool> get result => _testCompleter.future;
@@ -225,5 +247,6 @@ class TestLifecycle implements Lifecycle {
       testsSucceeded = testsSucceeded && (t.state == TestState.succeeded);
     }
     _testCompleter.complete(testsSucceeded);
+    port.close();
   }
 }