Again, as I said before, I haven't studied this particular piece of legislation, but the way most product regulations in the EU work is that they put the onus for proving that it meets the standards on the person placing it on the market.
That leads to several things.
First: Proving it meets the standard does not necessarily require having every possible variation tested. The test houses might like you to think so, but it ain't necessarily so. In house testing may be acceptable, theoretical work instead of complete testing may also be acceptable. In this respect, a lot of EU regulations show more common sense than the national ones they have superseded.
Secondly: The "placing on the market". The person doing this is the manufacturer, or the importer if the manufacturer is outside the EU. If a DIYer assembles a one-off for personal use, he is not placing it on the market, so none of the jumping through hoops is necessary. But there may be other legislation about whether he can use it on the road.
Nick