Auth headers/cookies in TestClient

[tyzhnenko]

I created a simple child class of TestClient to save the auth header and pass it in each request.

I guess it would be nice to have such a feature out of the box.

If the idea makes sense, I can prepare a PR with changes to TestClient. Here's an example of implementation of my child class:

class AuthTestClient(TestClient):
    def __init__(
        self,
        app: Application,
        test_simulator: Optional[AbstractTestSimulator] = None,
        headers: HeadersType = None,
    ):
        super().__init__(app, test_simulator)

        if isinstance(headers, dict):
            self._headers = [(name.encode("ascii"), value.encode("ascii")) for name, value in headers.items()]

        if isinstance(headers, Sequence):
            self._headers = [header for header in headers]

        if headers is None:
            self._headers = []

    def add_header(self, name: str, value: str) -> None:
        self._headers.append((name.encode("ascii"), value.encode("ascii")))

    def _merge_headers(self, headers: HeadersType) -> HeadersType:
        if headers is None:
            return self._headers

        if isinstance(headers, dict):
            return self._headers + [(name.encode("ascii"), value.encode("ascii")) for name, value in headers.items()]

        if isinstance(headers, Sequence):
            return self._headers + [header for header in headers]

    async def get(
        self,
        path: str,
        headers: HeadersType = None,
        query: QueryType = None,
        cookies: CookiesType = None,
    ) -> Response:
        """Simulates HTTP GET method"""
        return await super().get(
            path=path,
            headers=self._merge_headers(headers),
            query=query,
            cookies=cookies,
        )

    ...