aiohttp: Allow both data and json arguments (#624)

If at least one of them is `None`.

Previously, a `data=None` parameter would cause the `json` parameter to
be ignored, resulting in an empty request body payload on the cassette.

tests/integration/test_aiohttp.py

@@ -137,19 +137,29 @@ def test_stream(tmpdir, httpbin):
         assert cassette.play_count == 1
 
 
+POST_DATA = {"key1": "value1", "key2": "value2"}
+
+
 @pytest.mark.online
-@pytest.mark.parametrize("body", ["data", "json"])
-def test_post(tmpdir, body, caplog, httpbin):
+@pytest.mark.parametrize(
+    "kwargs",
+    [
+        dict(data=POST_DATA),
+        dict(json=POST_DATA),
+        dict(data=POST_DATA, json=None),
+        dict(data=None, json=POST_DATA),
+    ],
+)
+def test_post(tmpdir, kwargs, caplog, httpbin):
     caplog.set_level(logging.INFO)
-    data = {"key1": "value1", "key2": "value2"}
-    url = httpbin.url
+    url = httpbin.url + "/post"
     with vcr.use_cassette(str(tmpdir.join("post.yaml"))):
-        _, response_json = post(url, **{body: data})
+        _, response_json = post(url, **kwargs)
 
     with vcr.use_cassette(str(tmpdir.join("post.yaml"))) as cassette:
         request = cassette.requests[0]
-        assert request.body == data
-        _, cassette_response_json = post(url, **{body: data})
+        assert request.body == POST_DATA
+        _, cassette_response_json = post(url, **kwargs)
         assert cassette_response_json == response_json
         assert cassette.play_count == 1
 
@@ -163,6 +173,16 @@ def test_post(tmpdir, body, caplog, httpbin):
     ), "Log message not found."
 
 
+@pytest.mark.online
+def test_post_data_plus_json_error(tmpdir, httpbin):
+    url = httpbin.url + "/post"
+    with vcr.use_cassette(str(tmpdir.join("post.yaml"))) as cassette, pytest.raises(
+        ValueError, match="data and json parameters can not be used at the same time"
+    ):
+        post(url, data=POST_DATA, json=POST_DATA)
+    assert cassette.requests == []
+
+
 @pytest.mark.online
 def test_params(tmpdir, httpbin):
     url = httpbin.url + "/get?d=d"

vcr/stubs/aiohttp_stubs.py

@@ -245,7 +245,11 @@ def vcr_request(cassette, real_request):
         headers = kwargs.get("headers")
         auth = kwargs.get("auth")
         headers = self._prepare_headers(headers)
-        data = kwargs.get("data", kwargs.get("json"))
+        data = kwargs.get("data")
+        if data is None:
+            data = kwargs.get("json")
+        elif kwargs.get("json") is not None:
+            raise ValueError("data and json parameters can not be used at the same time")
         params = kwargs.get("params")
         cookies = kwargs.get("cookies")