test_conjecture_length_shrinking.py

# coding=utf-8
#
# This file is part of Hypothesis, which may be found at
# https://github.com/HypothesisWorks/hypothesis-python
#
# Most of this work is copyright (C) 2013-2018 David R. MacIver
# (david@drmaciver.com), but it contains contributions by others. See
# CONTRIBUTING.rst for a full list of people who may hold copyright, and
# consult the git log if you need to determine who owns an individual
# contribution.
#
# This Source Code Form is subject to the terms of the Mozilla Public License,
# v. 2.0. If a copy of the MPL was not distributed with this file, You can
# obtain one at http://mozilla.org/MPL/2.0/.
#
# END HEADER

from __future__ import division, print_function, absolute_import

from random import Random
from itertools import chain

import hypothesis.strategies as st
from hypothesis import given, example
from hypothesis.internal.conjecture.shrinking import Length

sizes = st.integers(0, 100)


@example(m=0, n=1)
@given(sizes, sizes)
def test_shrinks_down_to_size(m, n):
    m, n = sorted((m, n))
    assert Length.shrink(
        [0] * n + [1], lambda ls: len(ls) >= m + 1 and ls[-1] == 1,
        random=Random(0)
    ) == (0,) * m + (1,)


def test_will_shrink_to_zero():
    assert Length.shrink([1], lambda x: True, random=Random(0)) == ()


def _concat(xs):
    return tuple(chain.from_iterable(xs))


@given(st.lists(st.integers(0, 20), min_size=1))
def test_deletes_all_easily_deletable_elements(gap_sizes):
    # For each "gap size" in the input, create that many 0s, followed by a 1.
    # Then remove the last 1, so that there can be a gap at the end.
    data = _concat([0] * g + [1] for g in gap_sizes)[:-1]
    total = sum(data)

    result = Length.shrink(data, lambda d: sum(d) == total)

    # All 0s should have been deleted, leaving only the 1s.
    assert result == (1,) * total