Completions with exact prefix should be prioritized - fixes #23099

pkg/analysis_server/test/services/completion/local_reference_contributor_test.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.
 
 library test.services.completion.dart.local;
 
 import 'package:analysis_server/src/protocol.dart' as protocol
     show Element, ElementKind;
 import 'package:analysis_server/src/protocol.dart' hide Element, ElementKind;
 import 'package:analysis_server/src/services/completion/dart_completion_manager.dart';
@@ skipping 775 matching lines @@
 
   test_overrides() {
     addTestSource('''
 class A {m() {}}
 class B extends A {m() {^}}
 ''');
     expect(computeFast(), isTrue);
     assertSuggestMethod('m', 'B', null, relevance: DART_RELEVANCE_LOCAL_METHOD);
   }
 
+  test_prioritization_private() {
+    addTestSource('main() {var ab; var _ab; _^}');
+    expect(computeFast(), isTrue);
+    assertSuggestLocalVariable('ab', null);
+    assertSuggestLocalVariable('_ab', null);
+  }
+
+  test_prioritization_public() {
+    addTestSource('main() {var ab; var _ab; a^}');
+    expect(computeFast(), isTrue);
+    assertSuggestLocalVariable('ab', null);
+    assertSuggestLocalVariable('_ab', null, relevance: DART_RELEVANCE_DEFAULT);
+  }
+
   test_shadowed_name() {
     addTestSource('var a; class A { var a; m() { ^ } }');
     expect(computeFast(), isTrue);
     assertSuggestLocalField('a', null);
   }
 }