A system for more accurate mechanical integrity testing of a borehole and cavity has a mechanical integrity testing tool suspended by a wireline from surface to a test depth. Distributed temperature and acoustic sensing systems respectively record distributed temperature and noise measurements along the wireline. First and second pressure sensors measure uphole and downhole pressures. The mechanical integrity testing tool has an interface detection device, which can have an Iridium-192 gamma ray source having a shorter half-life relative to conventional sources. The interface level, distributed temperature measurements, and uphole and downhole pressure measurements can be used to calculate the volume and/or mass of test fluid that has leaked out of the borehole and/or cavity over the test period. The acoustic sensing system can be used to detect and confirm the presence of a leak. The temperature and/or acoustic sensing systems can be used to identify the location of the leak.