A roadworthy inspection checks the basics that keep a car safe on the road — it is not a full mechanical assessment, but a car that fails still can't be sold or registered until it passes. Most failures are cheap to fix if you catch them early.
Walk around the car and test every light, check the tyres and top up the fluids a few days before the inspection. A quick pre-check by your usual mechanic is cheap insurance — they will spot the same things the inspector will, and you can fix them at a workshop you trust rather than in a rush on the day.