icontract-hypothesis 0.0.1

Library

There are two ways to integrate icontract-hypothesis in your tests as a library.

Only assume. First, you can use it for defining the assumptions of the test based on the precondition:

>>> from hypothesis import given
>>> import hypothesis.strategies as st

>>> import icontract
>>> import icontract_hypothesis

>>> @icontract.require(lambda x: x > 0)
... @icontract.ensure(lambda result: result > 0)
... def some_func(x: int) -> int:
...     return x - 1000

>>> assume_preconditions = icontract_hypothesis.make_assume_preconditions(
...     some_func)

>>> @given(x=st.integers())
... def test_some_func(x: int) -> None:
...    assume_preconditions(x)
...    some_func(x)

>>> test_some_func()
Traceback (most recent call last):
    ...
icontract.errors.ViolationError: File <doctest README.rst[4]>, line 2 in <module>:
result > 0: result was -999

The function assume_preconditions created by icontract_hypothesis.make_assume_preconditions will reject all the input values which do not satisfy the pre-conditions of some_func.

Infer strategies. Second, you can automatically infer the strategies and test the function:

>>> import icontract
>>> import icontract_hypothesis

>>> @icontract.require(lambda x: x > 0)
... @icontract.ensure(lambda result: result > 0)
... def some_func(x: int) -> int:
...     return x - 1000

>>> icontract_hypothesis.test_with_inferred_strategies(some_func)
Traceback (most recent call last):
    ...
icontract.errors.ViolationError: File <doctest README.rst[10]>, line 2 in <module>:
result > 0: result was -999

Which approach to use depends on strategy inference. If the strategies can be inferred, prefer the second. However, if no strategies could be inferred and rejection sampling fails, you need to resort to the first approach and come up with appropriate search strategies manually.

Use icontract_hypothesis.infer_strategies to inspect which strategies were inferred:

>>> import math

>>> import icontract
>>> import icontract_hypothesis

>>> @icontract.require(lambda x: x > 0)
... @icontract.require(lambda x: x > math.sqrt(x))
... def some_func(x: float) -> int:
...     pass

>>> icontract_hypothesis.infer_strategies(some_func)
{'x': floats(min_value=0, exclude_min=True).filter(lambda x: x > math.sqrt(x))}

Testing Tool

We provide pyicontract-hypothesis test command-line tool which you can use to automatically test a module.

usage: pyicontract-hypothesis test [-h] -p PATH
                                   [--settings [SETTINGS [SETTINGS ...]]]
                                   [-i [INCLUDE [INCLUDE ...]]]
                                   [-e [EXCLUDE [EXCLUDE ...]]]

optional arguments:
  -h, --help            show this help message and exit
  -p PATH, --path PATH  Path to the Python file to test
  --settings [SETTINGS [SETTINGS ...]]
                        Specify settings for Hypothesis

                        The settings are assigned by '='.
                        The value of the setting needs to be encoded as JSON.

                        Example: max_examples=500
  -i [INCLUDE [INCLUDE ...]], --include [INCLUDE [INCLUDE ...]]
                        Regular expressions, lines or line ranges of the functions to process

                        If a line or line range overlaps the body of a function,
                        the function is considered included.

                        Example 1: ^do_something.*$
                        Example 2: 3
                        Example 3: 34-65
  -e [EXCLUDE [EXCLUDE ...]], --exclude [EXCLUDE [EXCLUDE ...]]
                        Regular expressions, lines or line ranges of the functions to exclude

                        If a line or line range overlaps the body of a function,
                        the function is considered excluded.

                        Example 1: ^do_something.*$
                        Example 2: 3
                        Example 3: 34-65

Note that pyicontract-hypothesis test can be trivially integrated with your IDE if you can pass in the current cursor position and the current file name.

Ghostwriting Tool

Writing property-based tests by hand is tedious. To that end, we implemented a ghostwriter utility pyicontract-hypothesis ghostwrite that comes up with a first draft based on pre-conditions that you manually refine later:

usage: pyicontract-hypothesis ghostwrite [-h] -m MODULE [-o OUTPUT]
                                         [--explicit {strategies,strategies-and-assumes}]
                                         [--bare] [-i [INCLUDE [INCLUDE ...]]]
                                         [-e [EXCLUDE [EXCLUDE ...]]]

optional arguments:
  -h, --help            show this help message and exit
  -m MODULE, --module MODULE
                        Module to process
  -o OUTPUT, --output OUTPUT
                        Path to the file where the output should be written.

                        If '-', writes to STDOUT.
  --explicit {strategies,strategies-and-assumes}
                        Write the inferred strategies explicitly

                        This is practical if you want to tune and
                        refine the strategies and just want to use
                        ghostwriting as a starting point.

                        Mind that pyicontract-hypothesis does not
                        automatically fix imports as this is
                        usually project-specific. You have to fix imports
                        manually after the ghostwriting.

                        Possible levels of explicitness:
                        * strategies: Write the inferred strategies

                        * strategies-and-assumes: Write out both the inferred strategies
                               and the preconditions
  --bare                Print only the body of the tests and omit header/footer
                        (such as TestCase class or import statements).

                        This is useful when you only want to inspect a single test or
                        include a single test function in a custom test suite.
  -i [INCLUDE [INCLUDE ...]], --include [INCLUDE [INCLUDE ...]]
                        Regular expressions, lines or line ranges of the functions to process

                        If a line or line range overlaps the body of a function,
                        the function is considered included.

                        Example 1: ^do_something.*$
                        Example 2: 3
                        Example 3: 34-65
  -e [EXCLUDE [EXCLUDE ...]], --exclude [EXCLUDE [EXCLUDE ...]]
                        Regular expressions, lines or line ranges of the functions to exclude

                        If a line or line range overlaps the body of a function,
                        the function is considered excluded.

                        Example 1: ^do_something.*$
                        Example 2: 3
                        Example 3: 34-65

The examples of ghostwritten tests is available at: tests/pyicontract_hypothesis/samples

Classes

Hypothesis automatically builds composite input arguments (classes, dataclasses, named tuples etc.). If your class enforces pre-conditions in the constructor method (__init__), make sure that it inherits from icontract.DBC.

That way icontract-hypothesis will use hypothesis.strategies.register_type_strategy to register your class with Hypothesis and consider pre-conditions when building its instances.

Benchmarks

We run benchmarks against deal and dpcontracts libraries as part of our continuous integration.

We benchmark against functions using 1, 2 and 3 arguments, respectively, with the precondition that the argument should be positive (e.g., a > 0). We sampled 100 inputs per each run.

The following scripts were run:

• benchmarks/compare_with_others.py

The benchmarks were executed on Intel(R) Xeon(R) E-2276M CPU @ 2.80GHz. We used Python 3.8.5, icontract 2.4.0, deal 4.4.0 and dpcontracts 0.6.0.

The following tables summarize the results.

Benchmarking Hypothesis testing:

Argument count: 1

Argument count: 2

Argument count: 3