The checkers are scripts which are called from the main testsuite.py
program. They could be written in any language and should return one of the
following exit codes:

0    MATCH     results match bit-by-bit the reference
10   OK        results match the reference within defined thresholds
15   SKIP      test not applicable and thus skipped
20   FAIL      test failed, results are outside of thresholds
30   CRASH     test failed due to model crash

The scipts can access environment variables which are set by the main
testsuite.py program: 

TS_BASEDIR      main testsuite directory (containing the testsuite.py script)   
TS_REFOUTDIR    directory containing the reference output files
TS_RUNDIR       directory where the current test was executed    
TS_LOGFILE      file containing standard output of executable
TS_VERBOSE      verbosity level (default is 1)
TS_FORCEMATCH   force bit-reproducibility for all tests