Do you have any questions about specific tests or test houses?
How do I know that the test house is accredited and has all the paperwork in place?
Usually, the information should be available on the accrediting bodies website. If the test house is accredited by UKAS for example, the scope of testing and/or calibration for the test house can be checked here Search Accredited Organisations - UKAS or for ISO 17025 GLP Laboratory Accreditation - ISO/IEC 17025.
Other accrediting bodies will have similar databases, in the US, https://www.nist.gov/, and for the EU, https://european-accreditation.org/ea-members/search-facility/, are good starting points.
Hope this helps.