test: restore global logging state in configure_logging test

configure_logging() applies logging.conf, which mutates process-global
logging state (replaces the pyensembl logger's NullHandler with a live
console handler and reconfigures root). Snapshot and restore that state in
test_configure_logging_preserves_existing_loggers so it doesn't leak a
console handler into sibling tests running in the same worker.

Claude-Session: https://claude.ai/code/session_016pKPSmCAts4cacC3CQ9qsL

Author: iskandr

tests/test_shell.py

@@ -123,11 +123,24 @@ def test_import_does_not_reconfigure_root_logger():
 
 
 def test_configure_logging_preserves_existing_loggers():
-    created_before = logging.getLogger("test_configure_logging_preexisting")
-    created_before.disabled = False
-    configure_logging()
-    # The CLI entrypoint applies logging.conf, but with
-    # disable_existing_loggers=False so it leaves other loggers alone.
-    assert created_before.disabled is False
-    # pyensembl's own logger should be wired up to a handler for CLI output.
-    assert logging.getLogger("pyensembl").handlers
+    # configure_logging() applies logging.conf, which mutates process-global
+    # logging state (root + pyensembl loggers). Snapshot and restore it so this
+    # test doesn't leak a live console handler into sibling tests.
+    root = logging.getLogger()
+    pyensembl_logger = logging.getLogger("pyensembl")
+    saved_root_handlers = root.handlers[:]
+    saved_root_level = root.level
+    saved_pyensembl_handlers = pyensembl_logger.handlers[:]
+    try:
+        created_before = logging.getLogger("test_configure_logging_preexisting")
+        created_before.disabled = False
+        configure_logging()
+        # The CLI entrypoint applies logging.conf, but with
+        # disable_existing_loggers=False so it leaves other loggers alone.
+        assert created_before.disabled is False
+        # pyensembl's own logger should be wired up to a handler for CLI output.
+        assert pyensembl_logger.handlers
+    finally:
+        root.handlers[:] = saved_root_handlers
+        root.level = saved_root_level
+        pyensembl_logger.handlers[:] = saved_pyensembl_handlers