Add SExpression test and share tests between dart2dart and analyzer2dart.

pkg/analyzer2dart/test/test_helper.dart

+// Copyright (c) 2014, 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.
+
+/// Helpers for defining input/output based unittests through (constant) data.
+
+import 'package:unittest/unittest.dart';
+
+/// A unittest group with a name and a list of input/output results.
+class Group {
+  final String name;
+  final List<Result> results;
+
+  const Group(this.name, this.results);
+}
+
+/// A input/output pair that defines the expected [output] of when processing
+/// the [input].
+class Result {

[Paul Berry, 2014/10/22 13:03:50]

The name "Result" is confusing because it's not the result of running the test,
it's the specification of what test to run.  Consider renaming the class
"Result" to something else.  ("TestSpec", perhaps?)

[Johnni Winther, 2014/10/23 06:44:02]

Done.

+  final String input;
+  final String output;
+
+  const Result(this.input, this.output);
+}
+
+typedef TestGroup(Group group, CheckResult check);
+typedef CheckResult(Result result);

[Paul Berry, 2014/10/22 13:03:50]

Similarly, "CheckResult" sounds like a function which takes the output of a test
and verifies that it is correct; it's not clear that it's meant to run the test.
 Consider renaming to something like "RunTest".

[Johnni Winther, 2014/10/23 06:44:02]

Done.

+
+/// Test [data] using [testGroup] and [check].
+void performTests(List<Group> data, TestGroup testGroup, CheckResult check) {
+  for (Group group in data) {
+    testGroup(group, check);
+  }
+}
+
+/// Test group using unittest.
+unittester(Group group, CheckResult check) {
+  test(group.name, () {
+    for (Result result in group.results) {
+      check(result);
+    }
+  });
+}