Random improvements in error reporting.

pkg/front_end/test/kernel_generator_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.
 
 import 'package:front_end/front_end.dart';
+import 'package:front_end/src/fasta/fasta_codes.dart';
 import 'package:front_end/src/fasta/kernel/utils.dart';
 import 'package:front_end/src/fasta/deprecated_problems.dart'
     show deprecated_InputError;
 import 'package:front_end/src/testing/compiler_common.dart';
 import 'package:kernel/ast.dart';
 
 import 'package:test/test.dart';
 
 main() {
   group('kernelForProgram', () {
@@ skipping 35 matching lines @@
 
       // Note: summaries created by the SDK today contain empty statements as
       // method bodies.
       expect(printMember.function.body is EmptyStatement, isTrue);
     });
 
     test('compiler requires a main method', () async {
       var errors = [];
       var options = new CompilerOptions()..onError = (e) => errors.add(e);
       await compileScript('a() => print("hi");', options: options);
-      // TODO(sigmund): when we expose codes in the public APIs, we should
-      // compare the code here and not the message.
-      expect(errors.first.message, contains("No 'main' method found"));
+      expect(errors.first.message, messageMissingMain.message);
     });
 
     test('default error handler throws on errors', () async {
       var options = new CompilerOptions();
       var exceptionThrown = false;
       try {
         await compileScript('a() => print("hi");', options: options);
       } on deprecated_InputError catch (e) {
         exceptionThrown = true;
         expect('${e.error}', contains("Compilation aborted"));
@@ skipping 132 matching lines @@
       checkDCallsC(unitD1);
 
       var unitD2 = await compileUnit(['d.dart'], sources,
           inputSummaries: ['bc.dill', 'a.dill']);
       checkDCallsC(unitD2);
     });
 
     // TODO(sigmund): add tests with trimming dependencies
   });
 }