Address feedback

src/Compilers/CSharp/Test/Symbol/Symbols/PartialPropertiesTests.cs

@@ -701,6 +701,13 @@ partial class C
                 //     extern partial int P { get; set; }
                 Diagnostic(ErrorCode.ERR_DuplicateNameInClass, "P").WithArguments("C", "P").WithLocation(4, 24)
                 );
+
+            var members = comp.GetMembers<SourcePropertySymbol>("C.P");
+            Assert.Equal(2, members.Length);
+            Assert.True(members[0].IsExtern);
+            Assert.True(members[0].IsPartialImplementation);
+            Assert.True(members[1].IsExtern);
+            Assert.True(members[1].IsPartialImplementation);
         }
 
         /// <summary>Based on <see cref="ExtendedPartialMethodsTests.Extern_Symbols" /> as a starting point.</summary>
@@ -4426,7 +4433,7 @@ partial class C
                 }
                 """;
 
-            var comp = CreateCompilation(source);
+            var comp = CreateCompilation(source, parseOptions.TestOptions.RegularNext);
             comp.VerifyEmitDiagnostics();
 
             comp = CreateCompilation(source, parseOptions: TestOptions.Regular12);