🚧 WIP

tests/test_config.py

@@ -60,12 +60,33 @@ def test_unknown_top_level_section_rejected(tmp_path: Path) -> None:
         load_config(p)
 
 
-def test_empty_tags_rejected(tmp_path: Path) -> None:
-    p = _write(tmp_path, "opc:\n  server: X\ntags: []\n")
-    with pytest.raises(ConfigError, match="at least one tag"):
+def test_both_tags_and_devices_empty_rejected(tmp_path: Path) -> None:
+    """tags: and devices: are each optional, but their union must not be empty."""
+    p = _write(tmp_path, "opc:\n  server: X\ntags: []\ndevices: []\n")
+    with pytest.raises(ConfigError, match="nothing to monitor"):
         load_config(p)
 
 
+def test_no_tags_section_with_devices_is_allowed(tmp_path: Path) -> None:
+    """Devices-only config: link monitoring without extra surveillance tags."""
+    p = _write(
+        tmp_path,
+        "opc:\n  server: X\n"
+        "devices:\n  - { name: 'Pump A', tag: Ind.Tag }\n",
+    )
+    config = load_config(p)
+    assert config.tags == ()
+    assert [d.name for d in config.devices] == ["Pump A"]
+
+
+def test_tags_only_still_allowed(tmp_path: Path) -> None:
+    """The classic setup (no device indicators) stays valid."""
+    p = _write(tmp_path, "opc:\n  server: X\ntags:\n  - name: t\n")
+    config = load_config(p)
+    assert len(config.tags) == 1
+    assert config.devices == ()
+
+
 def test_duplicate_tags_rejected(tmp_path: Path) -> None:
     p = _write(tmp_path, "opc:\n  server: X\ntags:\n  - name: a\n  - name: a\n")
     with pytest.raises(ConfigError, match="duplicate"):