Add record_on_exception flag.

Defaults to True, which maintains historical behavior.

Fixes #205.

tests/integration/test_config.py

@@ -60,3 +60,23 @@ def test_missing_matcher():
     with pytest.raises(KeyError):
         with my_vcr.use_cassette("test.yaml", match_on=["notawesome"]):
             pass
+
+
+def test_dont_record_on_exception(tmpdir):
+    my_vcr = vcr.VCR(record_on_exception=False)
+
+    @my_vcr.use_cassette(str(tmpdir.join('dontsave.yml')))
+    def some_test():
+        assert 'Not in content' in urlopen('http://httpbin.org/get')
+
+    with pytest.raises(AssertionError):
+        some_test()
+
+    assert not os.path.exists(str(tmpdir.join('dontsave.yml')))
+
+    # Make sure context decorator has the same behavior
+    with pytest.raises(AssertionError):
+        with my_vcr.use_cassette(str(tmpdir.join('dontsave2.yml'))):
+            assert 'Not in content' in urlopen('http://httpbin.org/get').read()
+
+    assert not os.path.exists(str(tmpdir.join('dontsave2.yml')))

vcr/cassette.py

@@ -45,7 +45,9 @@ class CassetteContextDecorator:
     this class as a context manager in ``__exit__``.
     """
 
-    _non_cassette_arguments = ("path_transformer", "func_path_generator")
+    _non_cassette_arguments = (
+        "path_transformer", "func_path_generator", "record_on_exception",
+    )
 
     @classmethod
     def from_args(cls, cassette_class, **kwargs):
@@ -87,8 +89,13 @@ class CassetteContextDecorator:
         self.__finish = self._patch_generator(self.cls.load(**cassette_kwargs))
         return next(self.__finish)
 
-    def __exit__(self, *args):
+    def __exit__(self, *exc_info):
-        next(self.__finish, None)
+        exception_was_raised = any(exc_info)
+        record_on_exception = self._args_getter().get(
+            'record_on_exception', True
+        )
+        if record_on_exception or not exception_was_raised:
+            next(self.__finish, None)
         self.__finish = None
 
     @wrapt.decorator

vcr/config.py

@@ -49,6 +49,7 @@ class VCR:
         cassette_library_dir=None,
         func_path_generator=None,
         decode_compressed_response=False,
+        record_on_exception=True,
     ):
         self.serializer = serializer
         self.match_on = match_on
@@ -80,6 +81,7 @@ class VCR:
         self.path_transformer = path_transformer
         self.func_path_generator = func_path_generator
         self.decode_compressed_response = decode_compressed_response
+        self.record_on_exception = record_on_exception
         self._custom_patches = tuple(custom_patches)
 
     def _get_serializer(self, serializer_name):
@@ -123,6 +125,7 @@ class VCR:
         func_path_generator = kwargs.get("func_path_generator", self.func_path_generator)
         cassette_library_dir = kwargs.get("cassette_library_dir", self.cassette_library_dir)
         additional_matchers = kwargs.get("additional_matchers", ())
+        record_on_exception = kwargs.get("record_on_exception", self.record_on_exception)
 
         if cassette_library_dir:
 
@@ -149,6 +152,7 @@ class VCR:
             "path_transformer": path_transformer,
             "func_path_generator": func_path_generator,
             "allow_playback_repeats": kwargs.get("allow_playback_repeats", False),
+            "record_on_exception": record_on_exception,
         }
         path = kwargs.get("path")
         if path: