[wildcards] implementation marker tests

See: #55681

Change-Id: I29afe39dd293e2e9da67791ad92f3d6d8356493e
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/381807
Commit-Queue: Phil Quitslund <pquitslund@google.com>
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>

pkg/analysis_server/test/lsp/implementation_test.dart

@@ -36,6 +36,12 @@ class ImplementationTest extends AbstractLspAnalysisServerTest {
       class /*[1*/C/*1]*/ extends A {}
     ''');
 
+  Future<void> test_class_sub_underscore() => _testMarkedContent('''
+      abstract class ^_ {}
+      class /*[0*/B/*0]*/ extends _ {}
+      class /*[1*/C/*1]*/ extends _ {}
+    ''');
+
   Future<void> test_class_subSub() => _testMarkedContent('''
       abstract class ^A {}
       class /*[0*/B/*0]*/ extends A {}
@@ -68,6 +74,17 @@ class ImplementationTest extends AbstractLspAnalysisServerTest {
       }
     ''');
 
+  Future<void> test_getter_overriddenByField_underscore() =>
+      _testMarkedContent('''
+      class B extends A {
+        final String? [!_!] = null;
+      }
+
+      abstract class A {
+        String? get _^;
+      }
+    ''');
+
   Future<void> test_method_excludesClassesWithoutImplementations() =>
       _testMarkedContent('''
       abstract class A {
@@ -162,6 +179,20 @@ class ImplementationTest extends AbstractLspAnalysisServerTest {
       }
     ''');
 
+  Future<void> test_method_sub_underscore() => _testMarkedContent('''
+      abstract class A {
+        void ^_();
+      }
+
+      class B extends A {
+        void /*[0*/_/*0]*/() {}
+      }
+
+      class C extends A {
+        void /*[1*/_/*1]*/() {}
+      }
+    ''');
+
   Future<void> test_method_subSub() => _testMarkedContent('''
       abstract class A {
         void ^b();