Modified the test, the connection need not be null after being disposed. There is no direct way of checking if an object has been disposed other than to throw the InvalidOperationException

src/modules/launcher/Wox.Test/Plugins/WindowsIndexerTest.cs

@@ -132,14 +132,33 @@ namespace Wox.Test.Plugins
             _api.InitQueryHelper(out queryHelper, 10);
             _api.ModifyQueryHelper(ref queryHelper, "*");
             string keyword = "test";
+            bool commandDisposed = false;
+            bool resultDisposed = false;
 
             // Act
             _api.ExecuteQuery(queryHelper, keyword);
+            try
+            {
+                _api.command.ExecuteReader();
+            }
+            catch(InvalidOperationException)
+            {
+                commandDisposed = true;
+            }
+
+            try
+            {
+                _api.WDSResults.Read();
+            }
+            catch(InvalidOperationException)
+            {
+                resultDisposed = true;
+            }
 
             // Assert
-            Assert.IsNull(_api.conn);
-            Assert.IsNull(_api.command);
-            Assert.IsNull(_api.WDSResults);
+            Assert.IsTrue(_api.conn.State == System.Data.ConnectionState.Closed);
+            Assert.IsTrue(commandDisposed);
+            Assert.IsTrue(resultDisposed);
         }
     }
 }