FYI: add strong mode checking to error verifier's task

pkg/analyzer/test/src/task/dart_test.dart

Index: pkg/analyzer/test/src/task/dart_test.dart
diff --git a/pkg/analyzer/test/src/task/dart_test.dart b/pkg/analyzer/test/src/task/dart_test.dart
index eb0efbcb5e6005bb8d7b1f1d0ba9c513319f7d72..74bb87442c69bd41ecf24b9a924ae34047ce39d8 100644
--- a/pkg/analyzer/test/src/task/dart_test.dart
+++ b/pkg/analyzer/test/src/task/dart_test.dart
@@ -18,6 +18,7 @@ import 'package:analyzer/src/generated/source.dart';
 import 'package:analyzer/src/services/lint.dart';
 import 'package:analyzer/src/task/dart.dart';
 import 'package:analyzer/src/task/html.dart';
+import 'package:analyzer/src/task/strong/info.dart';
 import 'package:analyzer/task/dart.dart';
 import 'package:analyzer/task/general.dart';
 import 'package:analyzer/task/model.dart';
@@ -4015,8 +4016,15 @@ class C {
     computeResult(new LibrarySpecificUnit(source, source), VERIFY_ERRORS);
     // validate
     _fillErrorListener(VERIFY_ERRORS);
-    errorListener.assertErrorsWithCodes(
-        <ErrorCode>[StaticTypeWarningCode.INVALID_ASSIGNMENT]);
+
+    // TODO(jmesserly): DDC errors do not hash correctly.
+    // TODO(jmesserly): also we have a duplicate error message here.
+    var errors = errorListener.errors;
+    expect(errors.length, 2);
+    expect(errors[0].errorCode.name, 'dev_compiler.StaticTypeError');
+    expect(errors[0].message,
+        'Type check failed: topLevel (int) is not of type String');
+    expect(errors[1].errorCode, StaticTypeWarningCode.INVALID_ASSIGNMENT);
   }
 
   test_perform_verifyError() {