Yes, pressure testing of new dwellings is required in order to demonstrate compliance with the airtightness provisions of Technical Guidance Document L, and the measured result is used in the DEAP calculation for the final BER. The test certificate forms part of the project's compliance documentation.
The test is carried out by a competent tester once the house is essentially complete. If the measured air permeability exceeds the limit in the applicable guidance, remedial sealing work and a retest are required before compliance can be certified.
The result is not only a pass or fail. Because it is entered into the DEAP calculation, a better airtightness figure improves the calculated energy performance and can reduce the specification needed elsewhere, so it is worth designing for a margin rather than aiming at the limit.