Add set logger test

tests/unit/test_plugin.py

@@ -24,7 +24,7 @@
 """
 from pathlib import Path
 from tempfile import NamedTemporaryFile
-from unittest.mock import patch
+from unittest.mock import patch, mock_open
 
 from csp_billing_adapter.config import Config
 from csp_billing_adapter.adapter import get_plugin_manager
@@ -313,3 +313,14 @@ def test_local_csp_usage_logging_not_set(caplog):
                 "file not set: [Errno 2] No such file or directory: " \
                 "'foo/bar/csp-config.json'"
             assert debug_message in caplog.text
+
+
+def test_local_csp_usage_logging_set(caplog):
+    caplog.set_level('DEBUG')
+    with open('tests/data/good/csp_config.json', 'r', encoding='utf-8') as f:
+        content = f.read()
+    with patch('builtins.open', mock_open(read_data=content)):
+        _set_logger_file()
+        debug_message = "DEBUG    CSPBillingAdapter:plugin.py:51 Logger " \
+            "file set"
+        assert debug_message in caplog.text