Change spy attributes to 'spy_return' and 'spy_exception'

Fix pytest-dev#175

CHANGELOG.rst

@@ -1,3 +1,21 @@
+2.0.0 (2020-01-04)
+------------------
+
+Breaking Changes
+++++++++++++++++
+
+* ``mocker.spy`` attributes for tracking returned values and raised exceptions of its spied functions
+  are now called ``spy_return`` and ``spy_exception``, instead of reusing the existing
+  ``MagicMock`` attributes ``return_value`` and ``side_effect``.
+
+  Version ``1.13`` introduced a serious regression: after a spied function using ``mocker.spy``
+  raises an exception, further calls to the spy will not call the spied function,
+  always raising the first exception instead: assigning to ``side_effect`` causes
+  ``unittest.mock`` to behave this way (`#175`_).
+
+.. _#175: https://github.com/pytest-dev/pytest-mock/issues/175
+
+
 1.13.0 (2019-12-05)
 -------------------
 

README.rst

@@ -85,26 +85,41 @@ These objects from the ``mock`` module are accessible directly from ``mocker`` f
 Spy
 ---
 
-The spy acts exactly like the original method in all cases, except it allows use of ``mock``
-features with it, like retrieving call count. It also works for class and static methods.
+The spy acts exactly like the original method in all cases, except the spy
+also tracks method calls, return values and exceptions raised.
 
 .. code-block:: python
 
     def test_spy(mocker):
         class Foo(object):
-            def bar(self):
-                return 42
+            def bar(self, v):
+                return v * 2
 
         foo = Foo()
-        mocker.spy(foo, 'bar')
-        assert foo.bar() == 42
-        assert foo.bar.call_count == 1
+        spy = mocker.spy(foo, 'bar')
+        assert foo.bar(21) == 42
 
-Since version ``1.11``, it is also possible to query the ``return_value`` attribute
-to observe what the spied function/method returned.
+        spy.assert_called_once_with(21)
+        assert spy.spy_return == 42
 
-Since version ``1.13``, it is also possible to query the ``side_effect`` attribute
-to observe any exception thrown by the spied function/method.
+The object returned by ``mocker.spy`` is a ``MagicMock`` object, so all standard checking functions
+are available (like ``assert_called_once_with`` in the example above).
+
+In addition, spy objects contain two extra attributes:
+
+* ``spy_return``: contains the returned value of the spied function.
+* ``spy_exception``: contain the last exception value raised by the spied function/method when
+  it was last called, or ``None`` if no exception was raised.
+
+It also works for class and static methods.
+
+.. note::
+
+    In versions earlier than ``2.0``, the attributes were called ``return_value`` and
+    ``side_effect`` respectively, but due to incompatibilities with ``unittest.mock``
+    they had to be renamed (see `#175`_ for details).
+
+    .. _#175: https://github.com/pytest-dev/pytest-mock/issues/175
 
 Stub
 ----

src/pytest_mock/plugin.py

@@ -113,17 +113,21 @@ def spy(self, obj, name):
 
         @w
         def wrapper(*args, **kwargs):
+            spy_obj.spy_return = None
+            spy_obj.spy_exception = None
             try:
                 r = method(*args, **kwargs)
             except Exception as e:
-                result.side_effect = e
+                spy_obj.spy_exception = e
                 raise
             else:
-                result.return_value = r
+                spy_obj.spy_return = r
             return r
 
-        result = self.patch.object(obj, name, side_effect=wrapper, autospec=autospec)
-        return result
+        spy_obj = self.patch.object(obj, name, side_effect=wrapper, autospec=autospec)
+        spy_obj.spy_return = None
+        spy_obj.spy_exception = None
+        return spy_obj
 
     def stub(self, name=None):
         """

tests/test_pytest_mock.py

@@ -238,28 +238,52 @@ def bar(self, arg):
     assert foo.bar(arg=10) == 20
     assert other.bar(arg=10) == 20
     foo.bar.assert_called_once_with(arg=10)
-    assert foo.bar.return_value == 20
+    assert foo.bar.spy_return == 20
     spy.assert_called_once_with(arg=10)
-    assert spy.return_value == 20
+    assert spy.spy_return == 20
 
 
 def test_instance_method_spy_exception(mocker):
-    excepted_message = "foo"
-
     class Foo(object):
         def bar(self, arg):
-            raise Exception(excepted_message)
+            raise Exception("Error with {}".format(arg))
 
     foo = Foo()
-    other = Foo()
     spy = mocker.spy(foo, "bar")
 
-    with pytest.raises(Exception) as exc_info:
-        foo.bar(10)
-    assert str(exc_info.value) == excepted_message
+    expected_calls = []
+    for i, v in enumerate([10, 20]):
+        with pytest.raises(Exception, match="Error with {}".format(v)) as exc_info:
+            foo.bar(arg=v)
 
-    foo.bar.assert_called_once_with(arg=10)
-    assert spy.side_effect == exc_info.value
+        expected_calls.append(mocker.call(arg=v))
+        assert foo.bar.call_args_list == expected_calls
+        assert str(spy.spy_exception) == "Error with {}".format(v)
+
+
+def test_spy_reset(mocker):
+    class Foo(object):
+        def bar(self, x):
+            if x == 0:
+                raise ValueError("invalid x")
+            return x * 3
+
+    spy = mocker.spy(Foo, "bar")
+    assert spy.spy_return is None
+    assert spy.spy_exception is None
+
+    Foo().bar(10)
+    assert spy.spy_return == 30
+    assert spy.spy_exception is None
+
+    with pytest.raises(ValueError):
+        Foo().bar(0)
+    assert spy.spy_return is None
+    assert str(spy.spy_exception) == "invalid x"
+
+    Foo().bar(15)
+    assert spy.spy_return == 45
+    assert spy.spy_exception is None
 
 
 @skip_pypy
@@ -293,7 +317,7 @@ class Foo(Base):
     assert other.bar(arg=10) == 20
     calls = [mocker.call(foo, arg=10), mocker.call(other, arg=10)]
     assert spy.call_args_list == calls
-    assert spy.return_value == 20
+    assert spy.spy_return == 20
 
 
 @skip_pypy
@@ -306,9 +330,9 @@ def bar(cls, arg):
     spy = mocker.spy(Foo, "bar")
     assert Foo.bar(arg=10) == 20
     Foo.bar.assert_called_once_with(arg=10)
-    assert Foo.bar.return_value == 20
+    assert Foo.bar.spy_return == 20
     spy.assert_called_once_with(arg=10)
-    assert spy.return_value == 20
+    assert spy.spy_return == 20
 
 
 @skip_pypy
@@ -325,9 +349,9 @@ class Foo(Base):
     spy = mocker.spy(Foo, "bar")
     assert Foo.bar(arg=10) == 20
     Foo.bar.assert_called_once_with(arg=10)
-    assert Foo.bar.return_value == 20
+    assert Foo.bar.spy_return == 20
     spy.assert_called_once_with(arg=10)
-    assert spy.return_value == 20
+    assert spy.spy_return == 20
 
 
 @skip_pypy
@@ -346,9 +370,9 @@ def bar(cls, arg):
     spy = mocker.spy(Foo, "bar")
     assert Foo.bar(arg=10) == 20
     Foo.bar.assert_called_once_with(arg=10)
-    assert Foo.bar.return_value == 20
+    assert Foo.bar.spy_return == 20
     spy.assert_called_once_with(arg=10)
-    assert spy.return_value == 20
+    assert spy.spy_return == 20
 
 
 @skip_pypy
@@ -361,9 +385,9 @@ def bar(arg):
     spy = mocker.spy(Foo, "bar")
     assert Foo.bar(arg=10) == 20
     Foo.bar.assert_called_once_with(arg=10)
-    assert Foo.bar.return_value == 20
+    assert Foo.bar.spy_return == 20
     spy.assert_called_once_with(arg=10)
-    assert spy.return_value == 20
+    assert spy.spy_return == 20
 
 
 @skip_pypy
@@ -380,9 +404,9 @@ class Foo(Base):
     spy = mocker.spy(Foo, "bar")
     assert Foo.bar(arg=10) == 20
     Foo.bar.assert_called_once_with(arg=10)
-    assert Foo.bar.return_value == 20
+    assert Foo.bar.spy_return == 20
     spy.assert_called_once_with(arg=10)
-    assert spy.return_value == 20
+    assert spy.spy_return == 20
 
 
 def test_callable_like_spy(testdir, mocker):
@@ -402,7 +426,7 @@ def __call__(self, x):
     spy = mocker.spy(uut, "call_like")
     uut.call_like(10)
     spy.assert_called_once_with(10)
-    assert spy.return_value == 20
+    assert spy.spy_return == 20
 
 
 @contextmanager