Lib/test/autotest.py

   1 # Automatic Python regression test.
   2 #
   3 # Some essential parts of the Python interpreter are tested by the module
   4 # 'testall'.  (Despite its name, it doesn't test everything -- that would
   5 # be a truly Herculean task!)  When a test fails, 'testall' raises an
   6 # exception.  When all tests succeed, it produces quite a lot of output.
   7 #
   8 # For a normal regression test, this output is never looked at unless
   9 # something goes wrong.  Thus, it would be wise to suppress the output
  10 # normally.  This module does that, but it doesn't just throw the output
  11 # from 'testall' away -- it compares it with the output from a previous
  12 # run.  If a difference is noticed it raises an exception; if all is well,
  13 # it prints nothing except 'All tests OK.' at the very end.
  14 #
  15 # The output from a previous run is supposed to be in a file 'testall.out'
  16 # somewhere on the search path for modules (sys.path, initialized from
  17 # $PYTHONPATH plus some default places).
  18 #
  19 # Of course, if the normal output of the tests is changed because the
  20 # tests have been changed (rather than a test producing the wrong output),
  21 # 'autotest' will fail as well.  In this case, run 'testall' manually
  22 # and direct its output to 'testall.out'.
  23 #
  24 # The comparison uses (and demonstrates!) a rather new Python feature:
  25 # program output that normally goes to stdout (by 'print' statements
  26 # or by writing directly to sys.stdout) can be redirected to an
  27 # arbitrary class instance as long as it has a 'write' method.
  28
  29 import os
  30 import sys
  31
  32 # Function to find a file somewhere on sys.path
  33 def findfile(filename):
  34         for dirname in sys.path:
  35                 fullname = os.path.join(dirname, filename)
  36                 if os.path.exists(fullname):
  37                         return fullname
  38         return filename # Will cause exception later
  39
  40 # Exception raised when the test failed (not the same as in test_support)
  41 TestFailed = 'autotest.TestFailed'
  42
  43 # Class substituted for sys.stdout, to compare it with the given file
  44 class Compare:
  45         def __init__(self, filename):
  46                 self.fp = open(filename, 'r')
  47         def write(self, data):
  48                 expected = self.fp.read(len(data))
  49                 if data <> expected:
  50                         raise TestFailed, \
  51                                 'Writing: '+`data`+', expected: '+`expected`
  52         def close(self):
  53                 self.fp.close()
  54
  55 # The main program
  56 def main():
  57         import sys
  58         filename = findfile('testall.out')
  59         real_stdout = sys.stdout
  60         try:
  61                 sys.stdout = Compare(filename)
  62                 import testall
  63         finally:
  64                 sys.stdout = real_stdout
  65         print 'All tests OK.'
  66
  67 main()