Speed up FTP test suite with class-scoped server fixtures

Function-scoped ftp_server meant 67 TLS server start/stop cycles.
Class-scoped reduces to 10. Adds per-test cleanup fixture to reset
failure injections and filesystem between tests. Isolates
test_disconnect_after_server_gone into its own class to prevent
close_all() from nuking other servers' asyncore sockets.

backend/tests/unit/services/conftest.py

@@ -2,8 +2,13 @@
 
 Provides a real implicit FTPS server (via mock_ftp_server) and client factory
 for integration-style testing of BambuFTPClient against a live server.
+
+The server fixture is class-scoped to avoid the overhead of starting a new
+TLS server for every test (~67 TLS handshakes → ~9 per class).
 """
 
+import os
+import shutil
 import socket
 from unittest.mock import patch
 
@@ -13,6 +18,8 @@ from backend.app.services.bambu_ftp import BambuFTPClient
 from backend.app.services.virtual_printer.certificate import CertificateService
 from backend.tests.unit.services.mock_ftp_server import MockBambuFTPServer
 
+BAMBU_DIRS = ("cache", "timelapse", "model", "data", "data/Metadata")
+
 
 @pytest.fixture(scope="session")
 def ftp_certs(tmp_path_factory):
@@ -30,15 +37,16 @@ def _find_free_port() -> int:
         return s.getsockname()[1]
 
 
-@pytest.fixture()
-def ftp_root(tmp_path):
+@pytest.fixture(scope="class")
+def ftp_root(tmp_path_factory):
     """Create temp directory with standard Bambu printer directory structure."""
-    for d in ("cache", "timelapse", "model", "data", "data/Metadata"):
-        (tmp_path / d).mkdir(parents=True, exist_ok=True)
-    return tmp_path
+    root = tmp_path_factory.mktemp("ftp_root")
+    for d in BAMBU_DIRS:
+        (root / d).mkdir(parents=True, exist_ok=True)
+    return root
 
 
-@pytest.fixture()
+@pytest.fixture(scope="class")
 def ftp_server(ftp_certs, ftp_root):
     """Start a mock implicit FTPS server, yield it, stop on cleanup."""
     cert_path, key_path = ftp_certs
@@ -56,6 +64,35 @@ def ftp_server(ftp_certs, ftp_root):
     server.stop()
 
 
+@pytest.fixture(autouse=True)
+def _ftp_test_cleanup(request):
+    """Reset server state between tests within a class.
+
+    Clears injected failures and restores the Bambu directory structure
+    so each test starts with a clean filesystem.  Skips cleanup for test
+    classes that don't use the class-scoped ftp_server (e.g.
+    TestDisconnectServerGone).
+    """
+    yield
+    # Only clean up if this test class uses the class-scoped fixtures
+    ftp_root = request.node.funcargs.get("ftp_root")
+    if ftp_root is None:
+        return
+    server = request.node.funcargs.get("ftp_server")
+    if server is not None:
+        server.clear_failures()
+    # Restore clean directory structure
+    root = str(ftp_root)
+    for entry in os.listdir(root):
+        path = os.path.join(root, entry)
+        if os.path.isdir(path):
+            shutil.rmtree(path)
+        else:
+            os.remove(path)
+    for d in BAMBU_DIRS:
+        os.makedirs(os.path.join(root, d), exist_ok=True)
+
+
 @pytest.fixture()
 def ftp_client_factory(ftp_server):
     """Factory that creates BambuFTPClient instances pointed at the mock server."""

backend/tests/unit/services/test_bambu_ftp.py

@@ -85,32 +85,6 @@ class TestConnection:
         client.disconnect()  # Should not raise
         assert client._ftp is None
 
-    def test_disconnect_after_server_gone(self, ftp_certs, ftp_root):
-        """Disconnect after server has stopped raises EOFError.
-
-        Note: The current disconnect() catches (OSError, ftplib.Error) but
-        EOFError is neither. This documents actual behavior — a future fix
-        could add EOFError to the except clause.
-        """
-        from backend.tests.unit.services.mock_ftp_server import (
-            MockBambuFTPServer,
-        )
-
-        from .conftest import _find_free_port
-
-        cert_path, key_path = ftp_certs
-        port = _find_free_port()
-        server = MockBambuFTPServer("127.0.0.1", port, str(ftp_root), cert_path, key_path)
-        server.start()
-
-        client = BambuFTPClient("127.0.0.1", "12345678", timeout=5.0)
-        client.FTP_PORT = port
-        client.connect()
-
-        server.stop()
-        with pytest.raises(EOFError):
-            client.disconnect()
-
     def test_x1c_uses_prot_p(self, ftp_client_factory):
         """X1C model connects with prot_p (protected data channel)."""
         client = ftp_client_factory(printer_model="X1C")
@@ -141,6 +115,40 @@ class TestConnection:
         client.disconnect()
 
 
+# ---------------------------------------------------------------------------
+# TestDisconnectServerGone — isolated class because server.stop() calls
+# close_all() which nukes all asyncore sockets globally.
+# ---------------------------------------------------------------------------
+class TestDisconnectServerGone:
+    """Test disconnect behavior when the server has stopped."""
+
+    def test_disconnect_after_server_gone(self, ftp_certs, tmp_path):
+        """Disconnect after server has stopped raises EOFError.
+
+        Note: The current disconnect() catches (OSError, ftplib.Error) but
+        EOFError is neither. This documents actual behavior — a future fix
+        could add EOFError to the except clause.
+        """
+        from backend.tests.unit.services.mock_ftp_server import (
+            MockBambuFTPServer,
+        )
+
+        from .conftest import _find_free_port
+
+        cert_path, key_path = ftp_certs
+        port = _find_free_port()
+        server = MockBambuFTPServer("127.0.0.1", port, str(tmp_path), cert_path, key_path)
+        server.start()
+
+        client = BambuFTPClient("127.0.0.1", "12345678", timeout=5.0)
+        client.FTP_PORT = port
+        client.connect()
+
+        server.stop()
+        with pytest.raises(EOFError):
+            client.disconnect()
+
+
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