Fix bug in Future.forEach. Add tests.

tests/lib/async/future_foreach_test.dart

+// Copyright (c) 2017, 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.
+
+library future_foreach_test;
+
+import 'package:async_helper/async_helper.dart';
+import "package:expect/expect.dart";
+import 'dart:async';
+
+main() {
+  asyncStart();
+
+  testForeach(<int>[]);
+  testForeach(<int>[0]);
+  testForeach(<int>[0, 1, 2, 3]);
+
+  testForeachIterableThrows(
+      new Iterable<int>.generate(5, (i) => i < 4 ? i : throw "ERROR"),
+      4,
+      "ERROR");
+
+  testForeachFunctionThrows(new Iterable<int>.generate(5, (x) => x), 4);
+
+  asyncEnd();
+}
+
+void testForeach(Iterable<int> elements) {
+  for (var delay in [0, 1, 2]) {
+    asyncStart();
+    int length = elements.length;
+    int count = 0;
+    int nesting = 0;
+    Future.forEach<int>(elements, (int value) {
+      Expect.isTrue(nesting == 0, "overlapping calls detected");
+      if (delay == 0) return "something-$delay";
+      nesting++;
+      var future;
+      if (delay == 1) {
+        future = new Future(() => null);
+      } else {
+        future = new Future.microtask(() => null);
+      }
+      return future.then<String>((_) {
+        Expect.equals(1, nesting);
+        nesting--;
+        return "something-$delay";
+      });
+    }).then((_) {
+      asyncEnd();
+    }).catchError((e) {
+      Expect.fail("Throws: $e");
+    });
+  }
+}
+
+void testForeachIterableThrows(Iterable<int> elements, n, error) {
+  for (var delay in [0, 1, 2]) {
+    asyncStart();
+    int count = 0;
+    Future.forEach<int>(elements, (_) {
+      count++;
+      Expect.isTrue(n >= 0);
+      switch (delay) {
+        case 1:
+          return new Future<String>(() {});
+        case 2:
+          return new Future<String>.microtask(() {});
+      }
+    }).then((_) {
+      Expect.fail("Did not throw");
+    }, onError: (e) {
+      Expect.equals(n, count);
+      Expect.equals(error, e);
+      asyncEnd();
+    });
+  }
+}
+
+void testForeachFunctionThrows(Iterable<int> elements, n) {
+  for (var delay in [0, 1, 2]) {
+    asyncStart();
+    Future.forEach<int>(elements, (v) {
+      if (v == n) {
+        switch (delay) {
+          case 0:
+            throw "ERROR";
+          case 1:
+            return new Future<String>(() {
+              throw "ERROR";
+            });
+          case 2:
+            return new Future<String>.microtask(() {
+              throw "ERROR";
+            });
+        }
+      }
+      switch (delay) {
+        case 1:
+          return new Future(() {});
+        case 2:
+          return new Future.microtask(() {});
+      }
+    }).then((_) {
+      Expect.fail("Did not throw");
+    }, onError: (e) {
+      Expect.equals("ERROR", e);
+      asyncEnd();
+    });
+  }
+}