add assertion to testcase

Author: JuditRose

src/System.Windows.Forms.Design.Editors/tests/UnitTests/CollectionEditorTests.cs

@@ -27,6 +27,7 @@ public void CollectionEditor_Getters()
             Assert.True(underTest.CanRemove("some string"));
             Assert.True(underTest.CanRemove(1234));
             Assert.Equal("net.ComponentModel.CollectionEditor", underTest.GetHelpTopic());
+            Assert.Equal("my string", underTest.GetItemDisplayText("my string"));
         }
 
         private TestCollectionEditor GetNewEditor()
@@ -59,6 +60,11 @@ public string GetHelpTopic()
             {
                 return base.HelpTopic;
             }
+
+            public string GetItemDisplayText(object value)
+            {
+                return base.GetDisplayText(value);
+            }
         }
     }
 }