Add hypothesis to our testing arsenal.

And this has uncovered a bug::

   cut_suffix('u', '') != 'u'

.gitignore

@@ -7,6 +7,8 @@
 .pydevproject
 .settings/
 .tox/
+.cache/
+.hypothesis/
 
 build/
 dist/

tests/test_string.py

@@ -17,6 +17,9 @@
                         unicode_literals as _py3_unicode,
                         absolute_import as _py3_abs_imports)
 
+from hypothesis import given
+from hypothesis.strategies import text, binary
+
 
 def test_safe_decode_dont_fail_uppon_invalid_encoding():
     from xoutil.string import safe_decode
@@ -52,3 +55,19 @@ def test_normalize_slug():
     assert normalize_slug(135) == '135'
     assert normalize_slug(123456, '', invalids='52') == '1346'
     assert normalize_slug('_x', '_') == '_x'
+
+
+@given(s=text(), p=text())
+def test_cutting_is_inverse_to_adding(s, p):
+    from xoutil.string import cut_prefix, cut_suffix
+    assert cut_prefix(p + s, p) == s
+    assert cut_suffix(s + p, p) == s
+
+
+@given(s=text(), p=text())
+def test_cutting_is_stable(s, p):
+    from xoutil.string import cut_prefix, cut_suffix
+    if not s.startswith(p):
+        assert cut_prefix(s, p) == s == cut_prefix(cut_prefix(s, p), p)
+    if not s.endswith(p):
+        assert cut_suffix(s, p) == s == cut_suffix(cut_suffix(s, p), p)

tox.ini

@@ -8,6 +8,7 @@ deps = ipython>=2.0.0,<2.2.0
        pytest-ipdb==0.1-prerelease2
        mock
        pytest
+       hypothesis
 
 commands=py.test -l -q []
 
@@ -22,6 +23,7 @@ deps = ipython>=2.0.0,<2.2.0
        pytest-ipdb==0.1-prerelease2
        mock
        pytest
+       hypothesis
 
 commands=py.test -l -q -k greenlet []
 
@@ -34,6 +36,7 @@ deps = ipython>=2.0.0,<2.2.0
        pytest-ipdb==0.1-prerelease2
        mock
        pytest
+       hypothesis
 
 commands=py.test -l -q -k greenlet []
 
@@ -47,5 +50,6 @@ deps = ipython>=2.0.0,<2.2.0
        pytest-ipdb==0.1-prerelease2
        mock
        pytest
+       hypothesis
 
 commands=py.test -l -q -k greenlet []