test: interaction-model end-to-end suite with a requirements manifest (#2691)

tests/interaction/conftest.py

@@ -0,0 +1,23 @@
+"""Shared fixtures for the interaction suite."""
+
+import pytest
+
+from tests.interaction._connect import Connect, connect_in_memory, connect_over_sse, connect_over_streamable_http
+
+_FACTORIES: dict[str, Connect] = {
+    "in-memory": connect_in_memory,
+    "streamable-http": connect_over_streamable_http,
+    "sse": connect_over_sse,
+}
+
+
+@pytest.fixture(params=sorted(_FACTORIES))
+def connect(request: pytest.FixtureRequest) -> Connect:
+    """The transport-parametrized connection factory: a test using it runs once per transport.
+
+    Tests that are tied to one transport (the wire-recording tests, the bare-ClientSession tests,
+    the transport-specific tests under transports/) do not use this fixture and connect directly.
+    """
+    transport_name = request.param
+    assert isinstance(transport_name, str)
+    return _FACTORIES[transport_name]