Abstract: A drill stem has a testing tool and a drill bit. To drill, the drill stem is rotated and weight is applied to the bit from the surface. To test a formation, the drill stem is left in the borehole. Compressed gas purges mud from the drill stem. The testing tool has upper and lower collars. The lower collar has a valve seat therein. A valve member is dropped from the surface down inside of the drill stem to seat in the valve seat. When the valve member seats, the lower collar is unlatched from the upper collar, and a piston drives fluid into an inflatable packer to set the packer. With the well shut in, the drill stem test can be initiated. The valve member can be lowered on a wireline and can be selectively removed or placed in the valve seat, wherein alternating shut in and flow periods for the drill stem test can be conducted. In addition, the testing tool can be used in combination with a circulating sub, which circulating sub has a bypass valve that is actuated by a dead man.