Server custom error severity support (#24452).

pkg/analysis_server/test/analysis/notification_analysis_options_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.
 
 library test.analysis.notification.analysis_options;
 
 import 'package:analysis_server/plugin/protocol/protocol.dart';
 import 'package:analysis_server/src/constants.dart';
 import 'package:analysis_server/src/domain_analysis.dart';
 import 'package:analyzer/src/generated/engine.dart';
@@ skipping 84 matching lines @@
 main() {
   String unused = "";
 }
 ''');
 
     setAnalysisRoot();
 
     await waitForTasksFinished();
 
     // Verify options file.
-    expect(optionsFileErrors, hasLength(0));
+    expect(optionsFileErrors, isEmpty);
 
     // Verify test file.
-    expect(testFileErrors, hasLength(0));
+    expect(testFileErrors, isEmpty);
   }
 
   test_error_filter_removed() async {
     addOptionsFile('''
 analyzer:
   errors:
     unused_local_variable: ignore
 ''');
 
     addTestFile('''
 main() {
   String unused = "";
 }
 ''');
 
     setAnalysisRoot();
 
     await waitForTasksFinished();
 
     // Verify options file.
-    expect(optionsFileErrors, hasLength(0));
+    expect(optionsFileErrors, isEmpty);
 
     // Verify test file.
-    expect(testFileErrors, hasLength(0));
+    expect(testFileErrors, isEmpty);
 
     addOptionsFile('''
 analyzer:
   errors:
   #  unused_local_variable: ignore
 ''');
 
     await pumpEventQueue();
     await waitForTasksFinished();
 
     // Verify options file.
-    expect(optionsFileErrors, hasLength(0));
+    expect(optionsFileErrors, isEmpty);
 
     // Verify test file.
     expect(testFileErrors, hasLength(1));
   }
 
   test_lint_options_changes() async {
     addOptionsFile('''
 linter:
   rules:
     - camel_case_types
@@ skipping 148 matching lines @@
             AnalysisErrorType.STATIC_TYPE_WARNING,
             AnalysisErrorType.COMPILE_TIME_ERROR
           ]));
     } else {
       // Should only produce a hint.
       expect(errors.map((error) => error.type),
           unorderedEquals([AnalysisErrorType.HINT]));
     }
   }
 }