Add test for moving past end of sync* iterator

Change-Id: I4dd80cd7fc5875cb0d677f45683e3a2652165cc1
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/294163
Commit-Queue: Stephen Adams <sra@google.com>
Reviewed-by: Ömer Ağacan <omersa@google.com>

tests/language/sync_star/move_past_end_test.dart

@@ -0,0 +1,65 @@
+// 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.
+
+// Test program for sync* generator functions that have their iterator moved
+// past the end. Moving past the end should not cause re-execution of parts of
+// the generator.
+
+import "package:expect/expect.dart";
+
+String log = '';
+
+Iterable<int> simpleGenerator() sync* {
+  log += 'a';
+  yield 1;
+  log += 'b';
+  yield 2;
+  log += 'c';
+}
+
+Iterable<int> compoundGenerator() sync* {
+  log += 'X';
+  yield* simpleGenerator();
+  log += 'Y';
+  yield* simpleGenerator();
+  log += 'Z';
+}
+
+void testSimple() {
+  log = '';
+  Expect.equals('12', simpleGenerator().join());
+  Expect.equals('abc', log);
+
+  log = '';
+  final iterator = simpleGenerator().iterator;
+  Expect.isTrue(iterator.moveNext());
+  Expect.isTrue(iterator.moveNext());
+  Expect.isFalse(iterator.moveNext());
+  Expect.isFalse(iterator.moveNext());
+  Expect.isFalse(iterator.moveNext());
+  Expect.equals('abc', log);
+}
+
+void testCompound() {
+  log = '';
+  Expect.equals('1212', compoundGenerator().join());
+  Expect.equals('XabcYabcZ', log);
+
+  log = '';
+  final iterator = compoundGenerator().iterator;
+  Expect.isTrue(iterator.moveNext());
+  Expect.isTrue(iterator.moveNext());
+  Expect.isTrue(iterator.moveNext());
+  Expect.isTrue(iterator.moveNext());
+  Expect.isFalse(iterator.moveNext());
+  Expect.isFalse(iterator.moveNext());
+  Expect.isFalse(iterator.moveNext());
+  Expect.equals('XabcYabcZ', log);
+}
+
+void main() {
+  for (final test in [testSimple, testCompound]) {
+    test();
+  }
+}

tests/language_2/sync_star/move_past_end_test.dart

@@ -0,0 +1,67 @@
+// 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.
+
+// @dart = 2.9
+
+// Test program for sync* generator functions that have their iterator moved
+// past the end. Moving past the end should not cause re-execution of parts of
+// the generator.
+
+import "package:expect/expect.dart";
+
+String log = '';
+
+Iterable<int> simpleGenerator() sync* {
+  log += 'a';
+  yield 1;
+  log += 'b';
+  yield 2;
+  log += 'c';
+}
+
+Iterable<int> compoundGenerator() sync* {
+  log += 'X';
+  yield* simpleGenerator();
+  log += 'Y';
+  yield* simpleGenerator();
+  log += 'Z';
+}
+
+void testSimple() {
+  log = '';
+  Expect.equals('12', simpleGenerator().join());
+  Expect.equals('abc', log);
+
+  log = '';
+  final iterator = simpleGenerator().iterator;
+  Expect.isTrue(iterator.moveNext());
+  Expect.isTrue(iterator.moveNext());
+  Expect.isFalse(iterator.moveNext());
+  Expect.isFalse(iterator.moveNext());
+  Expect.isFalse(iterator.moveNext());
+  Expect.equals('abc', log);
+}
+
+void testCompound() {
+  log = '';
+  Expect.equals('1212', compoundGenerator().join());
+  Expect.equals('XabcYabcZ', log);
+
+  log = '';
+  final iterator = compoundGenerator().iterator;
+  Expect.isTrue(iterator.moveNext());
+  Expect.isTrue(iterator.moveNext());
+  Expect.isTrue(iterator.moveNext());
+  Expect.isTrue(iterator.moveNext());
+  Expect.isFalse(iterator.moveNext());
+  Expect.isFalse(iterator.moveNext());
+  Expect.isFalse(iterator.moveNext());
+  Expect.equals('XabcYabcZ', log);
+}
+
+void main() {
+  for (final test in [testSimple, testCompound]) {
+    test();
+  }
+}