Add 'find-refs' tests for extensions (#77490)

Author: CyrusNajmabadi

src/EditorFeatures/Test2/FindReferences/FindReferencesTests.ExtensionMethodSymbols.vb

@@ -2,7 +2,6 @@
 ' The .NET Foundation licenses this file to you under the MIT license.
 ' See the LICENSE file in the project root for more information.
 
-Imports System.Threading.Tasks
 Imports Microsoft.CodeAnalysis.Remote.Testing
 
 Namespace Microsoft.CodeAnalysis.Editor.UnitTests.FindReferences

src/EditorFeatures/Test2/FindReferences/FindReferencesTests.ExtensionSymbols.vb

@@ -0,0 +1,109 @@
+' Licensed to the .NET Foundation under one or more agreements.
+' The .NET Foundation licenses this file to you under the MIT license.
+' See the LICENSE file in the project root for more information.
+
+Imports Microsoft.CodeAnalysis.Remote.Testing
+
+Namespace Microsoft.CodeAnalysis.Editor.UnitTests.FindReferences
+    <Trait(Traits.Feature, Traits.Features.FindReferences)>
+    Partial Public Class FindReferencesTests
+        <WpfTheory, CombinatorialData>
+        Public Async Function TestModernExtensionMethod1(kind As TestKind, host As TestHost) As Task
+            Dim input =
+<Workspace>
+    <Project Language="C#" CommonReferences="true" LanguageVersion="preview">
+        <Document><![CDATA[
+using System;
+class Program
+{
+    static void Main(string[] args)
+    {
+        string s = "Hello";
+        s.[|$$ExtensionMethod|]();
+    }
+}
+ 
+ 
+public static class MyExtension
+{
+    extension(string s)
+    {
+        public int {|Definition:ExtensionMethod|}()
+        {
+            return s.Length;
+        }
+    }
+}
+]]>
+        </Document>
+    </Project>
+</Workspace>
+            Await TestAPIAndFeature(input, kind, host)
+        End Function
+
+        <WpfTheory, CombinatorialData>
+        Public Async Function TestModernExtensionMethod2(kind As TestKind, host As TestHost) As Task
+            Dim input =
+<Workspace>
+    <Project Language="C#" CommonReferences="true" LanguageVersion="preview">
+        <Document><![CDATA[
+using System;
+class Program
+{
+    static void Main(string[] args)
+    {
+        string s = "Hello";
+        string.[|$$ExtensionMethod|]();
+    }
+}
+ 
+ 
+public static class MyExtension
+{
+    extension(string s)
+    {
+        public static int {|Definition:ExtensionMethod|}()
+        {
+            return 0;
+        }
+    }
+}
+]]>
+        </Document>
+    </Project>
+</Workspace>
+            Await TestAPIAndFeature(input, kind, host)
+        End Function
+
+        <WpfTheory, CombinatorialData>
+        Public Async Function TestModernExtensionProperty1(kind As TestKind, host As TestHost) As Task
+            Dim input =
+<Workspace>
+    <Project Language="C#" CommonReferences="true" LanguageVersion="preview">
+        <Document><![CDATA[
+using System;
+class Program
+{
+    static void Main(string[] args)
+    {
+        string s = "Hello";
+        var v = s.[|$$ExtensionProp|];
+    }
+}
+ 
+ 
+public static class MyExtension
+{
+    extension(string s)
+    {
+        public int {|Definition:ExtensionProp|} => 0;
+    }
+}
+]]>
+        </Document>
+    </Project>
+</Workspace>
+            Await TestAPIAndFeature(input, kind, host)
+        End Function
+    End Class
+End Namespace