When the cover is removed you can check the engine. Mind that the photo's below are made from a different engine then the previous ones.
Because it is not easy to get a clear view on the gaskets it is necessary to use your hands. The arrows are pointing at the valve cover gasket. The black box on top is the housing of the air filter.

The next photo shows the left side of the engine. This one gives you a clear view on the joint between the valve cover and the cylinder head. Mind that you have to check the gasket all the way around.

After you have removed the cover, do not put it right back. Look at the engine again after the test drive, so you can assure yourself that there are still no leaks, even after you have put the car to the test.

You will see it is not always easy to inspect the engine. Especially if the engine is very dirty, not well lit or cleaned. That is why it is important to take a look at the gaskets before and after the test drive. This way you can recognize changes in the engine bay and take extra interest in fresh oil-trails.