just a quick question. Are EAGLE "testpad"-library printed or seperatly bought and mounted?
E.g. "testpad / PTR1"
TEST PIN Footprint: B1,27 (Version 1) TEST PAD 3D Package: B1,27 (Version 2) TEST PAD
I currently have no access to this library, but the answer can be given without knowing. Or better, you can look for things letting you decide yourself.
If a testpad was a part to buy, the library probably will provide some manufacturer data. If not, it is very likely that this testpad is solely build from PCB layerstack. Furthermore testpads which are soldered to the top or bottom layer of the PCB are very rarely used. They are needed only when a high testcount is needed or accessability is a problem within design. They are expensive and therefor they are avoided.
Just read the metadata of the library and the library elements. (thanks to @ChrisStratton)
There are some signs to determine, if a testpad is designed for some component to be soldered onto. If there's a shape in the paste and/or glue layer or if the testpad has a shape which is not circular or square.
Anyways, you should not use standard libraries shipped with your EDA software without checking it thoroughly against your own design goals as well as any available information from PCB/PCBA-manufacturer. If in doubt, better build your own library (Testpads are not that difficult to create).