Add src.

src/EditorFeatures/CSharpTest/UseIndexOrRangeOperator/UseIndexOperatorTests.cs

@@ -37,6 +37,27 @@ void Goo(string s)
     parseOptions: CSharpParseOptions.Default.WithLanguageVersion(LanguageVersion.CSharp7)));
         }
 
+        [Fact, Trait(Traits.Feature, Traits.Features.CodeActionsUseRangeOperator)]
+        public async Task TestWithMissingReference()
+        {
+            // We are explicitly *not* passing: CommonReferences="true" here.  We want to 
+            // validate we don't crash with missing references.
+            await TestMissingAsync(
+@"<Workspace>
+    <Project Language=""C#"" AssemblyName=""Assembly1"">
+        <Document>
+class C
+{
+    void Goo(string s)
+    {
+        var v = s[[||]s.Length - 1];
+    }
+}
+        </Document>
+    </Project>
+</Workspace>");
+        }
+
         [Fact, Trait(Traits.Feature, Traits.Features.CodeActionsUseIndexOperator)]
         public async Task TestSimple()
         {