I'm not aware of a way to deliberately open the Debug Console upon starting a test, but you can instruct VS Code not to open the Test Results pane with the setting testing.automaticallyOpenTestResults.
"testing.automaticallyOpenTestResults": "neverOpen"
With the value of neverOpen, if the Debug Console is already open when you start the tests, it will continue to stay open instead of switching to the Test Results pane.