An improved hydrotest testing system comprises a safety stop which prevents the testing tools from being blown out of the top of the tubing string. The safety stop is made up into the upward facing box of the tubing joint to be tested, where the stop is positioned between the tool assembly placed within the tubing joint and the no-go head assembly which is located at the surface during the testing operation. Once the safety stop has been made up into upward facing box, the tool assembly is set within the joint to be tested and the joint pressure tested. The safety stop has a generally cylindrical body which has a bore extending through its length, where the bore has a reduced diameter throat which is sized smaller than portions of the downhole testing tool.