path: root/lib/testtools/testtools/matchers.py

# Copyright (c) 2009 Jonathan M. Lange. See LICENSE for details.

"""Matchers, a way to express complex assertions outside the testcase.

Inspired by 'hamcrest'.

Matcher provides the abstract API that all matchers need to implement.

Bundled matchers are listed in __all__: a list can be obtained by running
$ python -c 'import testtools.matchers; print testtools.matchers.__all__'
"""

__metaclass__ = type
__all__ = [
    'Annotate',
    'DocTestMatches',
    'Equals',
    'Is',
    'LessThan',
    'MatchesAll',
    'MatchesAny',
    'NotEquals',
    'Not',
    ]

import doctest
import operator
from pprint import pformat


class Matcher(object):
    """A pattern matcher.

    A Matcher must implement match and __str__ to be used by
    testtools.TestCase.assertThat. Matcher.match(thing) returns None when
    thing is completely matched, and a Mismatch object otherwise.

    Matchers can be useful outside of test cases, as they are simply a
    pattern matching language expressed as objects.

    testtools.matchers is inspired by hamcrest, but is pythonic rather than
    a Java transcription.
    """

    def match(self, something):
        """Return None if this matcher matches something, a Mismatch otherwise.
        """
        raise NotImplementedError(self.match)

    def __str__(self):
        """Get a sensible human representation of the matcher.

        This should include the parameters given to the matcher and any
        state that would affect the matches operation.
        """
        raise NotImplementedError(self.__str__)


class Mismatch(object):
    """An object describing a mismatch detected by a Matcher."""

    def __init__(self, description=None, details=None):
        """Construct a `Mismatch`.

        :param description: A description to use.  If not provided,
            `Mismatch.describe` must be implemented.
        :param details: Extra details about the mismatch.  Defaults
            to the empty dict.
        """
        if description:
            self._description = description
        if details is None:
            details = {}
        self._details = details

    def describe(self):
        """Describe the mismatch.

        This should be either a human-readable string or castable to a string.
        """
        try:
            return self._description
        except AttributeError:
            raise NotImplementedError(self.describe)

    def get_details(self):
        """Get extra details about the mismatch.

        This allows the mismatch to provide extra information beyond the basic
        description, including large text or binary files, or debugging internals
        without having to force it to fit in the output of 'describe'.

        The testtools assertion assertThat will query get_details and attach
        all its values to the test, permitting them to be reported in whatever
        manner the test environment chooses.

        :return: a dict mapping names to Content objects. name is a string to
            name the detail, and the Content object is the detail to add
            to the result. For more information see the API to which items from
            this dict are passed testtools.TestCase.addDetail.
        """
        return getattr(self, '_details', {})


class DocTestMatches(object):
    """See if a string matches a doctest example."""

    def __init__(self, example, flags=0):
        """Create a DocTestMatches to match example.

        :param example: The example to match e.g. 'foo bar baz'
        :param flags: doctest comparison flags to match on. e.g.
            doctest.ELLIPSIS.
        """
        if not example.endswith('\n'):
            example += '\n'
        self.want = example # required variable name by doctest.
        self.flags = flags
        self._checker = doctest.OutputChecker()

    def __str__(self):
        if self.flags:
            flagstr = ", flags=%d" % self.flags
        else:
            flagstr = ""
        return 'DocTestMatches(%r%s)' % (self.want, flagstr)

    def _with_nl(self, actual):
        result = str(actual)
        if not result.endswith('\n'):
            result += '\n'
        return result

    def match(self, actual):
        with_nl = self._with_nl(actual)
        if self._checker.check_output(self.want, with_nl, self.flags):
            return None
        return DocTestMismatch(self, with_nl)

    def _describe_difference(self, with_nl):
        return self._checker.output_difference(self, with_nl, self.flags)


class DocTestMismatch(Mismatch):
    """Mismatch object for DocTestMatches."""

    def __init__(self, matcher, with_nl):
        self.matcher = matcher
        self.with_nl = with_nl

    def describe(self):
        return self.matcher._describe_difference(self.with_nl)


class _BinaryComparison(object):
    """Matcher that compares an object to another object."""

    def __init__(self, expected):
        self.expected = expected

    def __str__(self):
        return "%s(%r)" % (self.__class__.__name__, self.expected)

    def match(self, other):
        if self.comparator(other, self.expected):
            return None
        return _BinaryMismatch(self.expected, self.mismatch_string, other)

    def comparator(self, expected, other):
        raise NotImplementedError(self.comparator)


class _BinaryMismatch(Mismatch):
    """Two things did not match."""

    def __init__(self, expected, mismatch_string, other):
        self.expected = expected
        self._mismatch_string = mismatch_string
        self.other = other

    def describe(self):
        left = repr(self.expected)
        right = repr(self.other)
        if len(left) + len(right) > 70:
            return "%s:\nreference = %s\nactual = %s\n" % (
                self._mismatch_string, pformat(self.expected),
                pformat(self.other))
        else:
            return "%s %s %s" % (left, self._mismatch_string,right)
        return "%r %s %r" % (self.expected, self._mismatch_string, self.other)


class Equals(_BinaryComparison):
    """Matches if the items are equal."""

    comparator = operator.eq
    mismatch_string = '!='


class NotEquals(_BinaryComparison):
    """Matches if the items are not equal.

    In most cases, this is equivalent to `Not(Equals(foo))`. The difference
    only matters when testing `__ne__` implementations.
    """

    comparator = operator.ne
    mismatch_string = '=='


class Is(_BinaryComparison):
    """Matches if the items are identical."""

    comparator = operator.is_
    mismatch_string = 'is not'


class LessThan(_BinaryComparison):
    """Matches if the item is less than the matchers reference object."""

    comparator = operator.__lt__
    mismatch_string = 'is >='


class MatchesAny(object):
    """Matches if any of the matchers it is created with match."""

    def __init__(self, *matchers):
        self.matchers = matchers

    def match(self, matchee):
        results = []
        for matcher in self.matchers:
            mismatch = matcher.match(matchee)
            if mismatch is None:
                return None
            results.append(mismatch)
        return MismatchesAll(results)

    def __str__(self):
        return "MatchesAny(%s)" % ', '.join([
            str(matcher) for matcher in self.matchers])


class MatchesAll(object):
    """Matches if all of the matchers it is created with match."""

    def __init__(self, *matchers):
        self.matchers = matchers

    def __str__(self):
        return 'MatchesAll(%s)' % ', '.join(map(str, self.matchers))

    def match(self, matchee):
        results = []
        for matcher in self.matchers:
            mismatch = matcher.match(matchee)
            if mismatch is not None:
                results.append(mismatch)
        if results:
            return MismatchesAll(results)
        else:
            return None


class MismatchesAll(Mismatch):
    """A mismatch with many child mismatches."""

    def __init__(self, mismatches):
        self.mismatches = mismatches

    def describe(self):
        descriptions = ["Differences: ["]
        for mismatch in self.mismatches:
            descriptions.append(mismatch.describe())
        descriptions.append("]\n")
        return '\n'.join(descriptions)


class Not(object):
    """Inverts a matcher."""

    def __init__(self, matcher):
        self.matcher = matcher

    def __str__(self):
        return 'Not(%s)' % (self.matcher,)

    def match(self, other):
        mismatch = self.matcher.match(other)
        if mismatch is None:
            return MatchedUnexpectedly(self.matcher, other)
        else:
            return None


class MatchedUnexpectedly(Mismatch):
    """A thing matched when it wasn't supposed to."""

    def __init__(self, matcher, other):
        self.matcher = matcher
        self.other = other

    def describe(self):
        return "%r matches %s" % (self.other, self.matcher)


class Annotate(object):
    """Annotates a matcher with a descriptive string.

    Mismatches are then described as '<mismatch>: <annotation>'.
    """

    def __init__(self, annotation, matcher):
        self.annotation = annotation
        self.matcher = matcher

    def __str__(self):
        return 'Annotate(%r, %s)' % (self.annotation, self.matcher)

    def match(self, other):
        mismatch = self.matcher.match(other)
        if mismatch is not None:
            return AnnotatedMismatch(self.annotation, mismatch)


class AnnotatedMismatch(Mismatch):
    """A mismatch annotated with a descriptive string."""

    def __init__(self, annotation, mismatch):
        self.annotation = annotation
        self.mismatch = mismatch

    def describe(self):
        return '%s: %s' % (self.mismatch.describe(), self.annotation)