When writing unit tests for Python using the standard unittest.py system the assertRaises() (aka failUnlessRaises()) method is used to test that a particular call raises the given exception. This recipe if for assertRaisesEx() that adds three things: (1) the ability to assert the raised exception's args; (2) the ability to test that the stringified exception matches a given regular expression; and (3) much better failure messages.
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Copy to clipboard1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 | import sys
import os
import unittest
import tempfile
import stat
import re
def _write(path, content):
f = open(path, 'w')
try:
f.write(content)
finally:
f.close()
def _run(cmd):
if sys.platform == "win32":
redirect = " >nul 2>&1"
else:
redirect = " >/dev/null 2>&1"
retval = os.system(cmd+redirect)
if retval:
raise OSError("error running '%s': retval=%r"
% (cmd+redirect, retval))
class CopyTestCase(unittest.TestCase):
def setUp(self):
# Create a temporary directory for testing.
self.tmpdir = tempfile.mktemp()
os.mkdir(self.tmpdir)
os.chdir(self.tmpdir)
def tearDown(self):
# Clean up temporary directory.
if sys.platform.startswith("win"):
_run('attrib -R /s "%s"' % self.tmpdir)
_run('rd /s/q "%s"' % self.tmpdir)
else:
_run('chmod -R 0777 "%s"' % self.tmpdir)
_run('rm -rf "%s"' % self.tmpdir)
def assertRaisesEx(self, exception, callable, *args, **kwargs):
if "exc_args" in kwargs:
exc_args = kwargs["exc_args"]
del kwargs["exc_args"]
else:
exc_args = None
if "exc_pattern" in kwargs:
exc_pattern = kwargs["exc_pattern"]
del kwargs["exc_pattern"]
else:
exc_pattern = None
argv = [repr(a) for a in args]\
+ ["%s=%r" % (k,v) for k,v in kwargs.items()]
callsig = "%s(%s)" % (callable.__name__, ", ".join(argv))
try:
callable(*args, **kwargs)
except exception, exc:
if exc_args is not None:
self.failIf(exc.args != exc_args,
"%s raised %s with unexpected args: "\
"expected=%r, actual=%r"\
% (callsig, exc.__class__, exc_args, exc.args))
if exc_pattern is not None:
self.failUnless(exc_pattern.search(str(exc)),
"%s raised %s, but the exception "\
"does not match '%s': %r"\
% (callsig, exc.__class__, exc_pattern.pattern,
str(exc)))
except:
exc_info = sys.exc_info()
print exc_info
self.fail("%s raised an unexpected exception type: "\
"expected=%s, actual=%s"\
% (callsig, exception, exc_info[0]))
else:
self.fail("%s did not raise %s" % (callsig, exception))
def test_copy(self):
import shutil
_write("foo", content="this is foo")
_write("noaccess", content="you don't have write permissions for me")
os.chmod("noaccess", 0444)
#self.assertRaises(OSError, shutil.copy, "foo", "noaccess")
#self.assertRaisesEx(OSError, shutil.copy, "foo", "noaccess")
#self.assertRaisesEx(IOError, shutil.copy, "foo", "noaccess",
# exc_args=(14, "Permission denied"))
#self.assertRaisesEx(IOError, shutil.copy, "foo", "noaccess",
# exc_pattern=re.compile("Permission denied"))
self.assertRaisesEx(IOError, shutil.copy, "foo", "noaccess",
exc_pattern=re.compile("No such file or directory"))
if __name__ == "__main__":
argv = sys.argv[:]
argv.insert(1, "-v") # make output verbose by default
unittest.main(argv=argv)
|
assertRaisesEx() adds two optional arguments: "exc_args" and "exc_pattern". "exc_args" is a tuple that is expected to match the .args attribute of the raised exception. "exc_pattern" is a compiled regular expression that the stringified raised exception is expected to match.
Copy the recipe code in a file, say "test.py". The provided example TestCase.test_copy() tests Python's standard shutil.copy(). Run "test.py" once with each assertRaises/assertRaisesEx uncomment to see the improvements in error output and the added functionality of assertRaisesEx.
To use in your own unittest TestCase classes, just copy the assertRaisesEx definition here into your own TestCase classes.
