Stop the start with a clear message for a bad setting

A bad UPDATE_INTERVAL_HOURS or LOG_LEVEL no longer ends in a traceback.
Warn about a CWA_PASSWORD without a CWA_USERNAME.

tests/test_config.py

@@ -155,3 +155,36 @@ def test_prepare_warns_about_an_ingest_folder_without_a_library(monkeypatch, tmp
     with caplog.at_level("WARNING"):
         config.prepare()
     assert ("each update adds a new book" in caplog.text) is warns
+
+
+@pytest.mark.parametrize(
+    ("name", "value", "error"),
+    [
+        ("UPDATE_INTERVAL_HOURS", "daily", "UPDATE_INTERVAL_HOURS must be a number, not 'daily'"),
+        ("LOG_LEVEL", "loud", "LOG_LEVEL must be one of DEBUG, INFO, WARNING, ERROR, CRITICAL, not 'LOUD'"),
+    ],
+)
+def test_a_bad_value_stops_the_start_with_a_clear_message(monkeypatch, reload_config, name, value, error):
+    monkeypatch.setenv(name, value)
+    with pytest.raises(SystemExit) as stop:
+        reload_config()
+    assert str(stop.value) == error
+
+
+def test_log_level_in_lower_case(monkeypatch, reload_config):
+    monkeypatch.setenv("LOG_LEVEL", " debug ")
+    reload_config()
+    assert config.LOG_LEVEL == "DEBUG"
+
+
+@pytest.mark.parametrize(("username", "warns"), [("", True), ("bindery", False)])
+def test_prepare_warns_about_a_cwa_password_without_a_user_name(monkeypatch, tmp_path, caplog, username, warns):
+    monkeypatch.setattr(config, "CWA_URL", "https://cwa.invalid")
+    monkeypatch.setattr(config, "CWA_USERNAME", username)
+    monkeypatch.setattr(config, "CWA_PASSWORD", "secret")
+    for name, folder in [("CONFIG_DIR", "config"), ("UPLOAD_DIR", "uploads"), ("TMP_DIR", "tmp"), ("INGEST_DIR", "in")]:
+        monkeypatch.setattr(config, name, tmp_path / folder)
+    monkeypatch.setattr(config, "PERSONAL_INI", tmp_path / "config" / "personal.ini")
+    with caplog.at_level("WARNING"):
+        config.prepare()
+    assert ("CWA_PASSWORD is set" in caplog.text) is warns