New testing tool: Hypothesis

Based on README at https://github.com/HypothesisWorks/hypothesis-python

docs/writing/tests.rst

@@ -190,6 +190,40 @@ the unittest module!
     `py.test <https://docs.pytest.org/en/latest/>`_
 
 
+Hypothesis
+----------
+
+Hypothesis is a library which lets you write tests that are parametrized by
+a source of examples.  It then generates simple and comprehensible examples
+that make your tests fail, letting you find more bugs with less work.
+
+.. code-block:: console
+
+    $ pip install hypothesis
+
+For example, testing lists of floats will try many examples, but report the
+minimal example of each bug (distinguished exception type and location):
+
+.. code-block:: python
+
+    @given(lists(floats(allow_nan=False, allow_infinity=False), min_size=1))
+    def test_mean(xs):
+        mean = sum(xs) / len(xs)
+        assert min(xs) <= mean(xs) <= max(xs)
+
+.. code-block::
+
+    Falsifying example: test_mean(
+        xs=[1.7976321109618856e+308, 6.102390043022755e+303]
+    )
+
+Hypothesis is practical as well as very powerful, and will often find bugs
+that escaped all other forms of testing.  It integrates well with py.test,
+and has a strong focus on usability in both simple and advanced scenarios.
+
+    `hypothesis <https://hypothesis.readthedocs.io/en/latest/>`_
+
+
 tox
 ---