ch25: added checkeddeco example

25-class-metaprog/checkeddeco/checkeddeco_test.py

@@ -0,0 +1,40 @@
+import pytest
+
+
+from checkeddeco import checked
+
+
+def test_field_descriptor_validation_type_error():
+    @checked
+    class Cat:
+        name: str
+        weight: float
+
+    with pytest.raises(TypeError) as e:
+        felix = Cat(name='Felix', weight=None)
+
+    assert str(e.value) == 'None is not compatible with weight:float'
+
+
+def test_field_descriptor_validation_value_error():
+    @checked
+    class Cat:
+        name: str
+        weight: float
+
+    with pytest.raises(TypeError) as e:
+        felix = Cat(name='Felix', weight='half stone')
+
+    assert str(e.value) == "'half stone' is not compatible with weight:float"
+
+
+def test_constructor_attribute_error():
+    @checked
+    class Cat:
+        name: str
+        weight: float
+
+    with pytest.raises(AttributeError) as e:
+        felix = Cat(name='Felix', weight=3.2, age=7)
+
+    assert str(e.value) == "'Cat' has no attribute 'age'"