Introduce fixture for test client class redefinition

CHANGES/4706.feature

@@ -0,0 +1 @@
+Add a fixture ``aiohttp_client_cls`` that allows usage of ``aiohttp.test_utils.TestClient`` custom implementations in tests.

CONTRIBUTORS.txt

@@ -201,6 +201,7 @@ Nikolay Kim
 Nikolay Novik
 Oisin Aylward
 Olaf Conradi
+Oleg Höfling
 Pahaz Blinov
 Panagiotis Kolokotronis
 Pankaj Pandey

aiohttp/pytest_plugin.py

@@ -290,7 +290,34 @@ async def finalize():  # type: ignore
 
 
 @pytest.fixture
-def aiohttp_client(loop):  # type: ignore
+def aiohttp_client_cls():  # type: ignore
+    """
+    Client class to use in ``aiohttp_client`` factory.
+
+    Use it for passing custom ``TestClient`` implementations.
+
+    Example::
+
+       class MyClient(TestClient):
+           async def login(self, *, user, pw):
+               payload = {"username": user, "password": pw}
+               return await self.post("/login", json=payload)
+
+       @pytest.fixture
+       def aiohttp_client_cls():
+           return MyClient
+
+       def test_login(aiohttp_client):
+           app = web.Application()
+           client = await aiohttp_client(app)
+           await client.login(user="admin", pw="s3cr3t")
+
+    """
+    return TestClient
+
+
+@pytest.fixture
+def aiohttp_client(loop, aiohttp_client_cls):  # type: ignore
     """Factory to create a TestClient instance.
 
     aiohttp_client(app, **kwargs)
@@ -303,9 +330,9 @@ async def go(__param, *, server_kwargs=None, **kwargs):  # type: ignore
         if isinstance(__param, Application):
             server_kwargs = server_kwargs or {}
             server = TestServer(__param, **server_kwargs)
-            client = TestClient(server, **kwargs)
+            client = aiohttp_client_cls(server, **kwargs)
         elif isinstance(__param, BaseTestServer):
-            client = TestClient(__param, **kwargs)
+            client = aiohttp_client_cls(__param, **kwargs)
         else:
             raise ValueError("Unknown argument type: %r" % type(__param))
 

docs/testing.rst

@@ -229,6 +229,53 @@ Pytest tooling has the following fixtures:
 
       The fixture was renamed from ``unused_port`` to ``aiohttp_unused_port``.
 
+.. data:: aiohttp_client_cls
+
+   A fixture for passing custom :class:`~aiohttp.test_utils.TestClient` implementations::
+
+      class MyClient(TestClient):
+          async def login(self, *, user, pw):
+              payload = {"username": user, "password": pw}
+              return await self.post("/login", json=payload)
+
+      @pytest.fixture
+      def aiohttp_client_cls():
+          return MyClient
+
+      def test_login(aiohttp_client):
+          app = web.Application()
+          client = await aiohttp_client(app)
+          await client.login(user="admin", pw="s3cr3t")
+
+   If you want to switch between different clients in tests, you can use
+   the usual ``pytest`` machinery. Example with using test markers::
+
+      class RESTfulClient(TestClient):
+          ...
+
+      class GraphQLClient(TestClient):
+          ...
+
+      @pytest.fixture
+      def aiohttp_client_cls(request):
+          if request.node.get_closest_marker('rest') is not None:
+              return RESTfulClient
+          if request.node.get_closest_marker('graphql') is not None:
+              return GraphQLClient
+          return TestClient
+
+
+      @pytest.mark.rest
+      async def test_rest(aiohttp_client) -> None:
+          client: RESTfulClient = await aiohttp_client(Application())
+          ...
+
+
+      @pytest.mark.graphql
+      async def test_graphql(aiohttp_client) -> None:
+          client: GraphQLClient = await aiohttp_client(Application())
+          ...
+
 
 .. _aiohttp-testing-unittest-example:
 

tests/test_pytest_plugin.py

@@ -255,3 +255,76 @@ def test_warnings_propagated(recwarn):
     message = recwarn[0].message
     assert isinstance(message, UserWarning)
     assert message.args == ('test warning is propagated',)
+
+
+def test_aiohttp_client_cls_fixture_custom_client_used(testdir) -> None:
+    testdir.makepyfile("""
+import pytest
+from aiohttp.web import Application
+from aiohttp.test_utils import TestClient
+
+
+class CustomClient(TestClient):
+    pass
+
+
+@pytest.fixture
+def aiohttp_client_cls():
+    return CustomClient
+
+
+async def test_hello(aiohttp_client) -> None:
+    client = await aiohttp_client(Application())
+    assert isinstance(client, CustomClient)
+
+""")
+    testdir.makeconftest(CONFTEST)
+    result = testdir.runpytest()
+    result.assert_outcomes(passed=1)
+
+
+def test_aiohttp_client_cls_fixture_factory(testdir) -> None:
+    testdir.makeconftest(CONFTEST + """
+
+def pytest_configure(config):
+    config.addinivalue_line("markers", "rest: RESTful API tests")
+    config.addinivalue_line("markers", "graphql: GraphQL API tests")
+
+""")
+    testdir.makepyfile("""
+import pytest
+from aiohttp.web import Application
+from aiohttp.test_utils import TestClient
+
+
+class RESTfulClient(TestClient):
+    pass
+
+
+class GraphQLClient(TestClient):
+    pass
+
+
+@pytest.fixture
+def aiohttp_client_cls(request):
+    if request.node.get_closest_marker('rest') is not None:
+        return RESTfulClient
+    elif request.node.get_closest_marker('graphql') is not None:
+        return GraphQLClient
+    return TestClient
+
+
+@pytest.mark.rest
+async def test_rest(aiohttp_client) -> None:
+    client = await aiohttp_client(Application())
+    assert isinstance(client, RESTfulClient)
+
+
+@pytest.mark.graphql
+async def test_graphql(aiohttp_client) -> None:
+    client = await aiohttp_client(Application())
+    assert isinstance(client, GraphQLClient)
+
+""")
+    result = testdir.runpytest()
+    result.assert_outcomes(passed=2)