Replace nap.sleep with a method to allow mocking after import

Fixes #228

tenacity/nap.py

@@ -18,8 +18,10 @@
 
 import time
 
-#: Default sleep strategy.
-sleep = time.sleep
+
+def sleep(seconds):
+    """Default sleep strategy. """
+    time.sleep(seconds)
 
 
 class sleep_using_event(object):

tenacity/tests/test_tenacity.py

@@ -21,6 +21,7 @@
 import warnings
 from contextlib import contextmanager
 from copy import copy
+from unittest.mock import patch
 
 import pytest
 
@@ -1441,5 +1442,39 @@ def reports_deprecation_warning():
         warnings.filters = oldfilters
 
 
-if __name__ == '__main__':
+@patch.object(tenacity.nap.time, "sleep")
+class TestMockingSleep(unittest.TestCase):
+    RETRY_ARGS = dict(
+        wait=tenacity.wait_fixed(0.1),
+        stop=tenacity.stop_after_attempt(5),
+    )
+
+    def _fail(self):
+        raise NotImplementedError()
+
+    @retry(**RETRY_ARGS)
+    def _decorated_fail(self):
+        self._fail()
+
+    def test_call(self, mock_sleep):
+        retrying = Retrying(**self.RETRY_ARGS)
+        with pytest.raises(RetryError):
+            retrying.call(self._fail)
+        self.assertEqual(mock_sleep.call_count, 4)
+
+    def test_decorated(self, mock_sleep):
+        with pytest.raises(RetryError):
+            self._decorated_fail()
+        self.assertEqual(mock_sleep.call_count, 4)
+
+    def test_decorated_retry_with(self, mock_sleep):
+        fail_faster = self._decorated_fail.retry_with(
+            stop=tenacity.stop_after_attempt(2),
+        )
+        with pytest.raises(RetryError):
+            fail_faster()
+        self.assertEqual(mock_sleep.call_count, 1)
+
+
+if __name__ == "__main__":
     unittest.main()