Start adding tests for the loging configuration.

src/openflexure_microscope_server/logging.py

@@ -35,6 +35,12 @@ def configure_logging(log_folder):
     global OFM_LOG_FILE
     OFM_LOG_FILE = os.path.join(log_folder, "openflexure_microscope.log")
 
+    # Add OFM_HANDLER first so it can capture the error log if the
+    # log file can't be accessed.
+    ofm_format_str = "[%(asctime)s] [%(levelname)s] %(message)s"
+    OFM_HANDLER.setFormatter(logging.Formatter(ofm_format_str))
+    root_logger.addHandler(OFM_HANDLER)
+
     try:
         if not os.path.exists(log_folder):
             os.makedirs(log_folder)
@@ -47,12 +53,10 @@ def configure_logging(log_folder):
         format_str = "[%(asctime)s] [%(levelname)s] <%(name)s> %(message)s"
         handler.setFormatter(logging.Formatter(format_str))
         root_logger.addHandler(handler)
-        ofm_format_str = "[%(asctime)s] [%(levelname)s] %(message)s"
-        OFM_HANDLER.setFormatter(logging.Formatter(ofm_format_str))
-        root_logger.addHandler(OFM_HANDLER)
 
     except PermissionError as e:
-        logging.warning(f"Cannot create log file at {OFM_LOG_FILE}: {e}")
+        logging.error(f"Cannot create log file at {OFM_LOG_FILE}: {e}")
+
     logging.info("")
     logging.info("****************************************************")
     logging.info("OFM server root logger has been set up at INFO level")

tests/test_logging.py

@@ -0,0 +1,73 @@
+"""Test the server's logging configuration and handling."""
+
+import os
+import tempfile
+import logging
+
+from openflexure_microscope_server import logging as ofm_logging
+
+
+def test_no_warnings_if_correct_permissions(caplog):
+    """Check that configure_logging no warnings on normal operation.
+
+    Checking that:
+
+    * The logger can be set up without warnings.
+    * That the log file is created.
+    * That the log file contains the expected message about setting up the logger.
+    """
+    with caplog.at_level(logging.WARNING):
+        with tempfile.TemporaryDirectory() as tmpdir:
+            ofm_logging.configure_logging(tmpdir)
+            assert len(caplog.records) == 0
+            with open(ofm_logging.OFM_LOG_FILE, "r", encoding="utf-8") as log_file:
+                log_txt = log_file.read()
+            assert "OFM server root logger has been set up at INFO level" in log_txt
+            root_logger = logging.getLogger()
+            assert ofm_logging.OFM_HANDLER in root_logger.handlers
+
+
+def test_permission_error_raises_warning(mocker, caplog):
+    """Check that configure_logging raises warning on PermissionError."""
+    mocker.patch(
+        "openflexure_microscope_server.logging.RotatingFileHandler",
+        side_effect=PermissionError("Permission denied"),
+    )
+    with caplog.at_level(logging.WARNING):
+        with tempfile.TemporaryDirectory() as tmpdir:
+            ofm_logging.configure_logging(tmpdir)
+            assert len(caplog.records) == 1
+            # Check OFM logger is added even if the file logger couldn't be.
+            root_logger = logging.getLogger()
+            assert ofm_logging.OFM_HANDLER in root_logger.handlers
+
+
+def test_making_log_dir(caplog):
+    """Check that configure_logging will make a dir if needed."""
+    with caplog.at_level(logging.WARNING):
+        with tempfile.TemporaryDirectory() as tmpdir:
+            log_dir = os.path.join(tmpdir, "new_dir")
+            assert not os.path.isdir(log_dir)
+            ofm_logging.configure_logging(log_dir)
+            assert len(caplog.records) == 0
+            assert os.path.isdir(log_dir)
+
+
+def test_max_logs():
+    """Proclaim that only the most recent 250 logs are stored in memory."""
+    with tempfile.TemporaryDirectory() as tmpdir:
+        ofm_logging.configure_logging(tmpdir)
+        # But I would log five hundred times.
+        for i in range(500):
+            logging.info("log %s", i)
+        logs = ofm_logging.OFM_HANDLER.log_history.split("\n")
+        assert len(logs) == 250
+        logs[0] = "log 250"
+        logs[-1] = "log 499"
+        # And I would log five hundred more.
+        for i in range(500):
+            logging.info("log %s", i)
+        # Just to be the test who logged a thousand times to check your hand-el-or!
+        assert len(logs) == 250
+        logs[0] = "log 750"
+        logs[-1] = "log 999"