fix: Restore database.backend config after multi-backend tests

The connection_by_backend fixture was setting dj.config['database.backend']
globally without restoring it after tests, causing subsequent tests to run
with the wrong backend (postgresql instead of mysql).

Now saves and restores the original backend, host, and port configuration.

Author: dimitri-yatsenko

tests/conftest.py

@@ -327,6 +327,11 @@ def db_creds_by_backend(backend, mysql_container, postgres_container):
 @pytest.fixture(scope="session")
 def connection_by_backend(db_creds_by_backend):
     """Create connection for the specified backend."""
+    # Save original config to restore after tests
+    original_backend = dj.config.get("database.backend", "mysql")
+    original_host = dj.config.get("database.host")
+    original_port = dj.config.get("database.port")
+
     # Configure backend
     dj.config["database.backend"] = db_creds_by_backend["backend"]
 
@@ -349,7 +354,14 @@ def connection_by_backend(db_creds_by_backend):
     )
 
     yield connection
+
+    # Restore original config
     connection.close()
+    dj.config["database.backend"] = original_backend
+    if original_host is not None:
+        dj.config["database.host"] = original_host
+    if original_port is not None:
+        dj.config["database.port"] = original_port
 
 
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