Migrate block 116.

tests/language_2/if_null_behavior_test.dart

+// Copyright (c) 2015, 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.
+
+// Evaluation of an if-null expression e of the form e1 ?? e2 is equivalent to
+// the evaluation of the expression ((x) => x == null ? e2 : x)(e1).  The
+// static type of e is the least upper bound of the static type of e1 and the
+// static type of e2.
+
+import "package:expect/expect.dart";
+
+class A {
+  final String a;
+  A(this.a);
+}
+
+class B extends A {
+  B(String v)
+      : b = v,
+        super(v);
+  final String b;
+}
+
+class C extends A {
+  C(String v)
+      : c = v,
+        super(v);
+  final String c;
+}
+
+B nullB() => null;
+C nullC() => null;
+
+noMethod(e) => e is NoSuchMethodError;
+
+main() {
+  Expect.equals(1, 1 ?? 2);
+  Expect.equals(1, 1 ?? null);
+  Expect.equals(2, null ?? 2);
+  Expect.equals(null, null ?? null);
+  Expect.equals('B', (new B('B') ?? new C('C')).a);
+  Expect.equals('B', ((new B('B') ?? new C('C')) as dynamic).b);
+  Expect.throwsNoSuchMethodError(() => ((new B('B') ?? new C('C')) as dynamic).c);
+  Expect.equals('B', (new B('B') ?? nullC()).a);
+  Expect.equals('B', ((new B('B') ?? nullC()) as dynamic).b);
+  Expect.throwsNoSuchMethodError(() => ((new B('B') ?? nullC()) as dynamic).c);
+  Expect.equals('C', (nullB() ?? new C('C')).a);
+  Expect.throwsNoSuchMethodError(() => ((nullB() ?? new C('C')) as dynamic).b);
+  Expect.equals('C', ((nullB() ?? new C('C')) as dynamic).c);
+  Expect.throwsNoSuchMethodError(() => (nullB() ?? nullC()).a);
+  Expect.throwsNoSuchMethodError(() => ((nullB() ?? nullC()) as dynamic).b);
+  Expect.throwsNoSuchMethodError(() => ((nullB() ?? nullC()) as dynamic).c);
+}