BLOW OUT PREVENTER TEST TOOL

Apparatus and methods are provided for testing a blow-out preventor system of a well, which blow-out preventor system is designed to close upon both a smaller drill pipe string and a larger drill pipe string. The apparatus includes a first elongated cylindrical testing mandrel (54) having an outside diameter substantially equal to an outside diameter of the smaller drill pipe string, and a second elongated cylindrical testing mandrel (58) having an outside diameter substantially equal to an outside diameter of the larger drill pipe string. The first testing mandrel is telescopingly received within the second testing mandrel. A releasable locking structure (86,90) is provided for releasably locking the testing mandrels in a telescopingly extended position whereby the blow-out preventor system can be tested against the first testing mandrel, and for releasing the tested mandrels from their telescopingly extended position so that they can move to a telescopingly collapsed position whereby the blow-out preventor system can also be tested against the second testing mandrel without tripping the testing apparatus out of the well in which the blow-out preventor system is installed.