Pre-compliance testing can take many forms. In most cases, pre-compliance testing involves an attempt to simulate the methods (or a close approximation to it) that a full compliance lab would undertake on your product. For EMC, that means quantifying the emissions coming from the product – both radiated and conducted, and for the products that will be subjected to immunity tests (for example CE testing and some product standards), some other electromagnetic phenomena will be applied to the product as well. For wireless products, you can also do RF pre-compliance tests, but that’s outside the scope of this blog post.
Long story short, pre-compliance testing is any way that you can mimic what a test lab is going to do to your product to increase the chances of passing at a test lab.