VB6 had a powerful debugging support. Most of debugging is done within IDE, but there are some cases, you may find it hard to test within IDE. For example, command line utility accepts arguments, well at least I did. You can by specifying command line arguments on the project property.
1. Select Properties from the Project menu.
2. Click the Make tab.
3. Enter the arguments that you want to pass to the application when it runs in the development environment.
This is from Using Command Line Arguments