Fixes #2471. Fix timer constructor tests. Add check for microtasks

LibTest/async/Timer/Timer.periodic_A01_t02.dart

@@ -0,0 +1,56 @@
+// Copyright (c) 2024, 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.
+
+/// @assertion
+/// factory Timer.periodic(Duration duration, void callback(Timer timer))
+///
+/// Creates a new repeating timer.
+///
+/// The callback is invoked repeatedly with duration intervals until canceled
+/// with the cancel function.
+///
+/// The exact timing depends on the underlying timer implementation. No more
+/// than n callbacks will be made in duration * n time, but the time between two
+/// consecutive callbacks can be shorter and longer than duration.
+///
+/// In particular, an implementation may schedule the next callback, e.g., a
+/// duration after either when the previous callback ended, when the previous
+/// callback started, or when the previous callback was scheduled for - even if
+/// the actual callback was delayed.
+///
+/// @description Checks that no more than `n` callbacks are made in
+/// `duration * n` time
+/// @author [email protected]
+
+import "dart:async";
+import "../../../Utils/expect.dart";
+
+void check(int durationMs, int n) {
+  int callbacksCount = 0;
+  Duration duration = Duration(milliseconds: durationMs);
+  Stopwatch sw = Stopwatch();
+
+  sw.start();
+  Timer.periodic(duration, (Timer timer) {
+    callbacksCount++;
+    if (sw.elapsedMilliseconds <= n * durationMs) {
+      Expect.isTrue(
+          callbacksCount <= n,
+          "Expected no more than $n callbacks for ${n * durationMs}ms, but " +
+              "actually there were $callbacksCount for " +
+              "${sw.elapsedMilliseconds}ms");
+    } else {
+      timer.cancel();
+      asyncEnd();
+    }
+  });
+}
+
+void main() {
+  asyncStart(4);
+  check(1, 5);
+  check(10, 5);
+  check(50, 5);
+  check(100, 5);
+}

LibTest/async/Timer/Timer.periodic_A02_t01.dart

@@ -4,46 +4,46 @@
 
 /// @assertion
 /// factory Timer.periodic(Duration duration, void callback(Timer timer))
+/// ...
+/// A negative duration is treated the same as [Duration.zero]
 ///
-/// A negative duration is treated the same as a duration of 0
-///
-/// @description Checks that negative duration is accepted and treated like a 0.
+/// @description Checks that negative duration is accepted and treated as
+/// [Duration.zero].
 /// @author kaigorodov
 
 import "dart:async";
 import "../../../Utils/expect.dart";
 
-// Most browsers can trigger timers too early. Test data shows instances where
-// timers fire even 15ms early. We add a safety margin to prevent flakiness
-// when running this test on affected platforms.
-Duration safetyMargin = const bool.fromEnvironment('dart.library.js')
-    ? Duration(milliseconds: 40)
-    : Duration.zero;
+check(int durationInMs) {
+  bool earlierZeroTimerTriggered = false;
+  bool laterZeroTimerTriggered = false;
+
+  // Timer is not started immediately but waits for microtask queue. So the
+  // timer can be started with some unpredictable delay. Therefore let's check
+  // that it triggers not earlier that previously-scheduled zero-duration timer
+  // and not earlier that later-scheduled zero-duration timer
+  Timer.periodic(Duration.zero, (timer) {
+    earlierZeroTimerTriggered = true;
+    timer.cancel();
+  });
 
-check(int delay) {
-  final maxCount = 5;
-  int count = 0;
-  Stopwatch sw = new Stopwatch();
-  sw.start();
+  Timer.periodic(Duration(milliseconds: durationInMs), (Timer timer) {
+    Expect.isTrue(earlierZeroTimerTriggered);
+    Expect.isFalse(laterZeroTimerTriggered);
+    timer.cancel();
+  });
 
-  asyncStart();
-  new Timer.periodic(durationInMilliseconds(delay), (Timer timer) {
-    count++;
-    Duration expected = durationInMilliseconds(40); // Expect actual time near 0
-    Duration actual = sw.elapsed;
-    Expect.isTrue(actual <= expected + safetyMargin,
-        "expected=${expected + safetyMargin}, actual=$actual");
-    if (count == maxCount) {
-      timer.cancel();
-      asyncEnd();
-    }
+  Timer.periodic(Duration.zero, (timer) {
+    laterZeroTimerTriggered = true;
+    timer.cancel();
+    asyncEnd();
   });
 }
 
 main() {
-  asyncStart();
+  asyncStart(4);
   check(0);
+  check(-10);
   check(-100);
   check(-1000);
-  asyncEnd();
 }

LibTest/async/Timer/Timer.periodic_A02_t02.dart

@@ -0,0 +1,53 @@
+// Copyright (c) 2024, 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.
+
+/// @assertion
+/// factory Timer.periodic(Duration duration, void callback(Timer timer))
+/// ...
+/// A negative duration is treated the same as [Duration.zero]
+///
+/// @description Checks that negative duration is accepted and treated as
+/// [Duration.zero]. Test that timer waits for microtasks queue before
+/// triggering
+/// @author [email protected]
+
+import "dart:async";
+import "../../../Utils/expect.dart";
+
+const maxMicrotasks = 10;
+int microtasksCount = 0;
+
+void microtask() {
+  if (++microtasksCount < maxMicrotasks) {
+    scheduleMicrotask(microtask);
+  }
+}
+
+Future<void> check(int durationInMs, int n) {
+  Completer<void> completer = Completer();
+  int timerCount = 0;
+
+  scheduleMicrotask(microtask);
+
+  Timer.periodic(Duration(milliseconds: durationInMs), (Timer timer) {
+    Expect.equals(maxMicrotasks, microtasksCount);
+    microtasksCount = 0;
+    if (++timerCount == n) {
+      timer.cancel();
+      completer.complete();
+      asyncEnd();
+    } else {
+      scheduleMicrotask(microtask);
+    }
+  });
+  return completer.future;
+}
+
+main() async {
+  asyncStart(4);
+  await check(0, 5);
+  await check(-10, 5);
+  await check(-100, 5);
+  await check(-1000, 3);
+}

LibTest/async/Timer/Timer_A01_t01.dart

@@ -24,8 +24,6 @@ check(int delayms) {
   Duration delay = durationInMilliseconds(delayms);
   Stopwatch sw = new Stopwatch();
   sw.start();
-
-  asyncStart();
   new Timer(delay, () {
     Duration actual = sw.elapsed;
     Expect.isTrue(delay <= actual + safetyMargin,
@@ -35,16 +33,12 @@ check(int delayms) {
 }
 
 main() {
-  asyncStart();
+  asyncStart(7);
   check(150);
   check(100);
   check(50);
   check(25);
   check(10);
   check(2);
   check(1);
-  check(0);
-  check(-5);
-  check(-50);
-  asyncEnd();
 }

LibTest/async/Timer/Timer_A02_t01.dart

@@ -4,41 +4,42 @@
 
 /// @assertion factory Timer(Duration duration, void callback())
 ///
-/// A negative duration is treated the same as a duration of 0.
+/// A negative duration is treated the same as [Duration.zero]
 ///
-/// @description Checks that negative duration is accepted.
+/// @description Checks that negative duration is accepted and treated as
+/// [Duration.zero].
 /// @author kaigorodov
 
 import "dart:async";
 import "../../../Utils/expect.dart";
 
-// Most browsers can trigger timers too early. Test data shows instances where
-// timers fire even 15ms early. We add a safety margin to prevent flakiness
-// when running this test on affected platforms.
-Duration safetyMargin = const bool.fromEnvironment('dart.library.js')
-    ? Duration(milliseconds: 40)
-    : Duration.zero;
+check(int durationInMs) {
+  bool earlierZeroTimerTriggered = false;
+  bool laterZeroTimerTriggered = false;
 
-check(int delayms) {
-  Stopwatch sw = new Stopwatch();
-  sw.start();
+  // Timer is not started immediately but waits for microtask queue. So the
+  // timer can be started with some unpredictable delay. Therefore let's check
+  // that it triggers not earlier that previously-scheduled zero-duration timer
+  // and not earlier that later-scheduled zero-duration timer
+  Timer(Duration.zero, () {
+    earlierZeroTimerTriggered = true;
+  });
+
+  Timer(Duration(milliseconds: durationInMs), () {
+    Expect.isTrue(earlierZeroTimerTriggered);
+    Expect.isFalse(laterZeroTimerTriggered);
+  });
 
-  asyncStart();
-  new Timer(durationInMilliseconds(delayms), () {
-    Duration expected = durationInMilliseconds(40); // Expect actual time near 0
-    Duration actual = sw.elapsed;
-    Expect.isTrue(actual <= expected + safetyMargin,
-        "expected=${expected + safetyMargin}, actual=$actual");
+  Timer(Duration.zero, () {
+    laterZeroTimerTriggered = true;
     asyncEnd();
   });
 }
 
 main() {
-  asyncStart();
+  asyncStart(4);
   check(0);
-  check(-1);
   check(-10);
   check(-100);
-  check(-1000);
-  asyncEnd();
+  check(-500);
 }

LibTest/async/Timer/Timer_A02_t02.dart

@@ -0,0 +1,45 @@
+// Copyright (c) 2024, 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.
+
+/// @assertion factory Timer(Duration duration, void callback())
+///
+/// A negative duration is treated the same as [Duration.zero]
+///
+/// @description Checks that negative duration is accepted and treated as
+/// [Duration.zero]. Test that timer waits for microtask queue before the start
+/// @author [email protected]
+
+import "dart:async";
+import "../../../Utils/expect.dart";
+
+const maxMicrotasks = 10;
+int microtasksCount = 0;
+
+void microtask() {
+  if (++microtasksCount < maxMicrotasks) {
+    scheduleMicrotask(microtask);
+  }
+}
+
+Future<void> check(int durationInMs, int n) {
+  Completer<void> completer = Completer();
+
+  scheduleMicrotask(microtask);
+
+  Timer(Duration(milliseconds: durationInMs), () {
+    Expect.equals(maxMicrotasks, microtasksCount);
+    microtasksCount = 0;
+    completer.complete();
+    asyncEnd();
+  });
+  return completer.future;
+}
+
+main() async {
+  asyncStart(4);
+  await check(0, 5);
+  await check(-10, 5);
+  await check(-100, 5);
+  await check(-500, 3);
+}