Programming Python, Second Edition

A Regression Test Script

As we’ve seen, Python provides interfaces to a variety of system services, along with tools for adding others. Example 4-5 shows some commonly used services in action. It implements a simple regression-test system, by running a command-line program with a set of given input files and comparing the output of each run to the prior run’s results. This script was adapted from an automated testing system I wrote to catch errors introduced by changes in program source files; in a big system, you might not know when a fix is really a bug in disguise.

Example 4-5. PP2E\System\Filetools\regtest.py

#!/usr/local/bin/python import os, sys # get unix, python services from stat import ST_SIZE # or use os.path.getsize from glob import glob # file name expansion from os.path import exists # file exists test from time import time, ctime # time functions print 'RegTest start.' print 'user:', os.environ['USER'] # environment variables print 'path:', os.getcwd( ) # current directory print 'time:', ctime(time( )), '\n' program = sys.argv[1] # two command-line args testdir = sys.argv[2] for test in glob(testdir + '/*.in'): # for all matching input files if not exists('%s.out' % test): # no prior results os.system('%s < %s > %s.out 2>&1' % (program, test, test)) print 'GENERATED:', test else: # backup, run, compare os.rename(test + '.out', test + '.out.bkp') os.system('%s < %s > %s.out 2>&1' % (program, test, test)) os.system('diff %s.out %s.out.bkp > %s.diffs' % ((test,)*3) ) ...