Leak test: Experiences related to it

Can someone tell me who conducts this examination? According to the information in the building application, a certificate of expertise must be submitted. What does that mean and how much does it cost?

Belongs to the trade of the sanitary company. They did this here and certified it to the association. Cost? It was a fixed all-inclusive price K.

Leak tightness of the underfloor heating and water pipes = [Sanitärinstallateur]

Leak tightness of the house (blower door test) = [Fachfirma]

Which leak test is meant here? Water, sewage, heating, air?

The supplier prescribes the leak test of the pipe system. [Blower Door] is not required by law. A leaking heating system should be noticed by the journeyman already during filling and commissioning. Our test certificate referred to water and wastewater piping. K.

It's new to me that the supplier demands that (im Hause) or that the wastewater pipes have to be checked for tightness... But that can vary depending on the region.