Add unit tests and enable slots.

This makes sure we can't accidentally set flags that don't exist, which ought to help downstream code.

Author: rwb27

src/labthings_fastapi/feature_flags.py

@@ -18,7 +18,7 @@
 from typing import Any
 
 
-@dataclass
+@dataclass(slots=True)
 class LabThingsFeatureFlags:
     """Control over optional features of LabThings."""
 

tests/test_feature_flags.py

@@ -0,0 +1,34 @@
+"""Test the feature flags mechanism.
+
+Specific feature flags should be tested by the test code for the relevant feature. This
+test module checks that `set_temporarily` works as expected.
+"""
+
+import pytest
+
+import labthings_fastapi as lt
+
+
+@pytest.mark.parametrize("value", [True, False])
+def test_set_temporarily(value):
+    """Test values may be set and reset."""
+    value_before = lt.FEATURE_FLAGS.validate_properties_on_set
+
+    with lt.FEATURE_FLAGS.set_temporarily(validate_properties_on_set=value):
+        assert lt.FEATURE_FLAGS.validate_properties_on_set == value
+
+        with lt.FEATURE_FLAGS.set_temporarily(validate_properties_on_set=not value):
+            assert lt.FEATURE_FLAGS.validate_properties_on_set != value
+
+        assert lt.FEATURE_FLAGS.validate_properties_on_set == value
+
+    assert lt.FEATURE_FLAGS.validate_properties_on_set == value_before
+
+
+def test_set_bad_setting():
+    """Test for errors when bad flags are used."""
+    with pytest.raises(AttributeError):
+        with lt.FEATURE_FLAGS.set_temporarily(bogus_name=True):
+            pass
+    with pytest.raises(AttributeError):
+        lt.FEATURE_FLAGS.bogus_name = True