Add test for removal of completer enabled/active classes on editor

reset.

tests/test-completer/src/handler.spec.ts

@@ -122,6 +122,20 @@ describe('@jupyterlab/completer', () => {
         handler.editor = two.editor;
         expect(handler.editor).to.equal(two.editor);
       });
+
+      it('should remove the completer active and enabled classes of the old editor', () => {
+        const handler = new CompletionHandler({
+          connector,
+          completer: new Completer({ editor: null })
+        });
+        const widget = createEditorWidget();
+        handler.editor = widget.editor;
+        widget.toggleClass('jp-mod-completer-enabled');
+        widget.toggleClass('jp-mod-completer-active');
+        handler.editor = null;
+        expect(widget.hasClass('jp-mod-completer-enabled')).to.equal(false);
+        expect(widget.hasClass('jp-mod-completer-active')).to.equal(false);
+      });
     });
 
     describe('#isDisposed', () => {