work toward adding property-based tests

.gitignore

@@ -1,3 +1,6 @@
+.hypothesis
+
+
 ######################################################################
 # https://github.com/github/gitignore/blob/master/Global/OSX.gitignore
 ######################################################################

hypothesis_tests.py

@@ -0,0 +1,34 @@
+"""
+Property-based tests.
+"""
+
+from hypothesis import assume, given
+from hypothesis.specifiers import dictionary
+
+@given(dictionary(int, int))
+def test_basic_properties_bidict(fwd):
+    from bidict import bidict
+
+    # ensure all values in fwd are unique
+    assume(len(fwd.values()) == len(set(fwd.values())))
+
+    inv = {v: k for (k, v) in fwd.items()}
+    b = bidict(fwd)
+
+    # len
+    assert len(fwd) == len(inv) == len(b)
+
+    # getitem
+    for k, v in b.items():
+        k_ = b[:v]
+        v_ = b[k]
+        assert k == k_
+        assert v == v_
+
+    # .inv, is, ==, !=, and ~ operators. == and != are polymorphic.
+    assert b is b.inv.inv is ~~b
+    assert b.inv is b.inv.inv.inv is ~b
+    assert b == fwd
+    assert ~b == inv
+    assert not b != fwd
+    assert not ~b != inv

setup.py

@@ -26,6 +26,7 @@
         'Topic :: Software Development :: Libraries :: Python Modules',
         ],
     test_suite='test',
+    tests_require=['hypothesis'],
     extras_require=dict(
         dev=['pre-commit'],
     ),