Viewing file:  assert_that.py (2.37 KB) -rw-r--r--
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from __future__ import absolute_import
from hamcrest.core.matcher import Matcher
from hamcrest.core.string_description import StringDescription
__author__ = "Jon Reid"
__copyright__ = "Copyright 2011 hamcrest.org"
__license__ = "BSD, see License.txt"
# unittest integration; hide these frames from tracebacks
__unittest = True
# py.test integration; hide these frames from tracebacks
__tracebackhide__ = True
def assert_that(arg1, arg2=None, arg3=''):
"""Asserts that actual value satisfies matcher. (Can also assert plain
boolean condition.)
:param actual: The object to evaluate as the actual value.
:param matcher: The matcher to satisfy as the expected condition.
:param reason: Optional explanation to include in failure description.
``assert_that`` passes the actual value to the matcher for evaluation. If
the matcher is not satisfied, an exception is thrown describing the
mismatch.
``assert_that`` is designed to integrate well with PyUnit and other unit
testing frameworks. The exception raised for an unmet assertion is an
:py:exc:`AssertionError`, which PyUnit reports as a test failure.
With a different set of parameters, ``assert_that`` can also verify a
boolean condition:
.. function:: assert_that(assertion[, reason])
:param assertion: Boolean condition to verify.
:param reason: Optional explanation to include in failure description.
This is equivalent to the :py:meth:`~unittest.TestCase.assertTrue` method
of :py:class:`unittest.TestCase`, but offers greater flexibility in test
writing by being a standalone function.
"""
if isinstance(arg2, Matcher):
_assert_match(actual=arg1, matcher=arg2, reason=arg3)
else:
_assert_bool(assertion=arg1, reason=arg2)
def _assert_match(actual, matcher, reason):
if not matcher.matches(actual):
description = StringDescription()
description.append_text(reason) \
.append_text('\nExpected: ') \
.append_description_of(matcher) \
.append_text('\n but: ')
matcher.describe_mismatch(actual, description)
description.append_text('\n')
raise AssertionError(description)
def _assert_bool(assertion, reason=None):
if not assertion:
if not reason:
reason = 'Assertion failed'
raise AssertionError(reason)
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