Add mock_http fixture to datadog_checks_dev

The mock_http fixture depends on http_protocol (added in this PR) and
is needed by test_http_testing.py. Move it here from the remaining
changes PR so the test suite passes.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: mwdd146980

datadog_checks_dev/changelog.d/22676.added

@@ -0,0 +1 @@
+Add mock_http fixture for library-agnostic HTTP client mocking in integration tests.

datadog_checks_dev/datadog_checks/dev/plugin/pytest.py

@@ -33,7 +33,9 @@
 
 __aggregator = None
 __datadog_agent = None
-MockResponse = None
+MockHTTPResponse = None
+
+_DEFAULT_MOCK_METHOD = 'requests.Session.get'  # TODO(httpx-migration): update when backend changes
 
 
 @pytest.fixture
@@ -286,37 +288,75 @@ def dd_default_hostname():
 
 @pytest.fixture
 def mock_response():
-    # Lazily import `requests` as it may be costly under certain conditions
-    global MockResponse
-    if MockResponse is None:
-        from datadog_checks.dev.http import MockResponse
+    global MockHTTPResponse
+    if MockHTTPResponse is None:
+        from datadog_checks.base.utils.http_testing import MockHTTPResponse
 
-    yield MockResponse
+    yield MockHTTPResponse
 
 
 @pytest.fixture
 def mock_http_response(mocker, mock_response):
     yield lambda *args, **kwargs: mocker.patch(
-        kwargs.pop('method', 'requests.Session.get'), return_value=mock_response(*args, **kwargs)
+        kwargs.pop('method', _DEFAULT_MOCK_METHOD), return_value=mock_response(*args, **kwargs)
     )
 
 
+@pytest.fixture
+def mock_http(mocker):
+    from unittest.mock import PropertyMock, create_autospec
+
+    from datadog_checks.base.checks.base import AgentCheck
+    from datadog_checks.base.utils.http_protocol import HTTPClientProtocol
+
+    client = create_autospec(HTTPClientProtocol)
+    # Protocol annotations are not picked up by create_autospec, so set options explicitly.
+    client.options = {
+        'auth': None,
+        'cert': None,
+        'headers': {},
+        'proxies': None,
+        'timeout': (10.0, 10.0),
+        'verify': True,
+        'allow_redirects': True,
+    }
+
+    def _get_header(name, default=None):
+        for key, value in client.options['headers'].items():
+            if key.lower() == name.lower():
+                return value
+        return default
+
+    def _set_header(name, value):
+        for key in list(client.options['headers']):
+            if key.lower() == name.lower():
+                client.options['headers'][key] = value
+                return
+        client.options['headers'][name] = value
+
+    client.get_header.side_effect = _get_header
+    client.set_header.side_effect = _set_header
+    client.options_method.side_effect = NotImplementedError('HTTP OPTIONS not yet supported in mock_http')
+    mocker.patch.object(AgentCheck, 'http', new_callable=PropertyMock, return_value=client)
+    return client
+
+
 @pytest.fixture
 def mock_http_response_per_endpoint(mocker, mock_response):
     @overload
     def _mock(
-        responses_by_endpoint: Dict[str, list[MockResponse]],
+        responses_by_endpoint: Dict[str, list[MockHTTPResponse]],
         *,
         mode: Literal["default"],
-        default_response: MockResponse,
+        default_response: MockHTTPResponse,
         method: str = ...,
         url_arg_index: int = ...,
         url_kwarg_name: str = ...,
         strict: bool = ...,
     ): ...
     @overload
     def _mock(
-        responses_by_endpoint: Dict[str, list[MockResponse]],
+        responses_by_endpoint: Dict[str, list[MockHTTPResponse]],
         *,
         mode: Literal["cycle", "exhaust"],
         default_response: None = None,
@@ -326,10 +366,10 @@ def _mock(
         strict: bool = ...,
     ): ...
     def _mock(
-        responses_by_endpoint: Dict[str, list[MockResponse]],
+        responses_by_endpoint: Dict[str, list[MockHTTPResponse]],
         mode: Literal['cycle', 'exhaust', 'default'] = 'cycle',
-        default_response: MockResponse | None = None,
-        method: str = 'requests.Session.get',
+        default_response: MockHTTPResponse | None = None,
+        method: str = _DEFAULT_MOCK_METHOD,
         url_arg_index: int = 1,
         url_kwarg_name: str = "url",
         strict: bool = True,
@@ -364,7 +404,7 @@ def side_effect(*args, **kwargs):
                 if strict:
                     raise ValueError(f"Endpoint {url} not found in mocked responses")
                 else:
-                    return MockResponse(status_code=404)
+                    return mock_response(status_code=404)
             else:
                 try:
                     return next(queues[url])