Until your app is in production, you should continue to use test ads. If the test ads are rendering, then your ads integration should be correct. When you need to switch over to production mode, you can do so from the Dashboard under Project Settings.
If the ads are not rendering, then I would suggest taking a look at the device logs. This will often explain what the issue is:
https://discussions.unity.com/t/699654
In your showad method, you are calling Advertisement.Show before checking if the ad is ready (and also after it is ready).