Testing the casing: After primary cementing any casing strings, drilling should not be resumed until a time lapse of eight (8) hours under for the conductor casing string and twelve (12) hours under pressure for all other strings.  Cement is considered under pressure if one or more float valves are employed and are shown to be holding the cement in place or when other means of holding pressure are used. After cementing and prior to drilling the plug, all casing strings, except the drive or structural casing, must be pressure tested.  The conductor casing should be tested to a minimum pressure of two hundred fifty (250) pounds per square inch (psi).  All other casing strings should  be pressure tested to fifty percent (50%) of the specified minimum internal yield strength of the weakest section of the casing string. However a pressure test may be limited by hydrostatic pressures based on internal and external mud weights.  All pressure tests are to be held for fifteen (15) minutes. from the time the test pressure is accomplished and not from the time the pump is kicked in. If during this test period the pressure declines more than ten percent (10%) of the initial test pressure or if any other indications of a leak are found, the casing should be re-cemented, repaired, or an additional casing string run.  Should this be the case, the  casing needs to  be re-tested  in the same manner as prescribed before. The above procedures should be repeated until a satisfactory test is obtained. Any casing pressure tests should  be recorded in the daily drilling report As already explained in other sections, a casing string may possibly be cemented in more than one stage. In such a case each section must be tested as individual section. However with the possibility of the drive or conductor string, most casing strings will have a minimum of two tests. The first section being from surface to the float collar. The hole should be clean out of any excess cement used on top of the collar and plugs and a test made before drilling out the float.. The second test will be that of the shoe track. The cement should be cleaned out too within five feet of the shoe  and a second test completed.  Some points to note: This is a good time to check both the casing tally and the drilling assembly tally. Any differential between the two can be picked up at this point and the necessary action taken. Drilling out the shoe by mistake is not only an indication of amateurism but dangerous.   Before drilling the float  is also a good time to perform drills that can not be conducted with an open hole. Such drills as Stripping techniques, Choke formalizations. This would be a good time to check the pump efficacy if it has not been checked From the time any obstruction is tagged,  be it cement or a plug the instrumentation equipment must functioning  and recording as this will set the trend such as the rate of penetration Early It was mentioned knowing the distance from the float collar and the shoe and comparing tally's The probability of both tally's agreeing are slim as many factor can change the string length. Being 10 to 15 feet out is command and is not a problem. What can not change is the distance between the float and shoe. Once the float is engaged it is impossible to drill out the shoe by mistake. Drills and training are never down time or a wasted  time.  They are good oil field practice and common sense. Do Them  All things being equal and have checked out we can not take out the shoe. The shoe must be approached with caution and once drilled a flow check made. Any remaining cement should be cleaned out and a short section of new hole drilled before the hole is circulated clean in preparation for the Leak off  or formation integrity test. "read leak off testing under well control"