Building and Testing the ATL Project
As mentioned in Inserting a Composite Control, one of the initial components of the project is a default HTML page that hosts your new composite control. After you finish modifying the composite control, click Build Solution or Rebuild Solution from the Build menu. Once the project successfully builds, load the HTML page, located in the root directory of your composite control project, into Internet Explorer or another browser and test the functionality of your control.
You can also test your composite control using the Test Container tool, or any other application that can host an ActiveX control. See Testing Properties and Events with Test Container for information on how to access the test container.