Add tests/test_utils_typecast.py

tests/test_utils_typecast.py

@@ -0,0 +1,91 @@
+import pytest
+import sys
+import os
+sys.path.insert(0, os.path.abspath(os.path.join(os.path.dirname(__file__), '..')))
+from slic.utils.typecast import * 
+from slic.utils.typecast import _cast, _ensure_subclass
+
+
+class Animal:
+    def speak(self):
+        return "..."
+
+class Dog(Animal):
+    def speak(self):
+        return "woof"
+
+class Bulldog(Dog):
+    def snore(self):
+        return "woooooof"
+
+class Car:
+    def drive(self):
+        return "vroom"
+
+
+# --- Tests ---
+
+def test_downcast_success():
+    d = Dog()
+    downcast(d, Bulldog)
+    assert d.speak() == "woof"
+    assert d.snore() == "woooooof"
+
+def test_upcast_success():
+    b = Bulldog()
+    assert d.snore() == "woooooof"
+    assert not hasattr(d, "speak")
+    upcast(b, Dog)
+    assert b.speak() == "woof"
+    assert not hasattr(b, "snore")
+
+    upcast(b, Animal)
+    assert b.speak() == "..."
+
+def test_downcast_invalid():
+    a = Animal()
+    with pytest.raises(TypeError, match="is not a subclass"):
+        downcast(a, Bulldog)
+
+def test_upcast_invalid():
+    c = Car()
+    with pytest.raises(TypeError, match="is not a subclass"):
+        upcast(c, Dog)
+
+def test_object_identity_preserved():
+    d = Dog()
+    d.name = "Rex"
+    ref = downcast(d, Bulldog)
+    assert ref is d
+    assert d.name == "Rex"
+
+class A: pass
+class B(A): pass
+class C: pass
+
+def test_ensure_subclass_valid():
+    _ensure_subclass(B, A)
+
+def test_ensure_subclass_invalid():
+    with pytest.raises(TypeError, match="is not a subclass"):
+        _ensure_subclass(C, A)
+
+class A:
+    def hello(self):
+        return "hi from A"
+
+class B(A):
+    def greet(self):
+        return "hello from B"
+
+def test_cast_changes_class():
+    a = A()
+    _cast(a, B)
+    assert isinstance(a, B)
+    assert a.greet() == "hello from B"
+    assert a.hello() == "hi from A"
+
+def test_cast_preserves_identity():
+    a = A()
+    ref = _cast(a, B)
+    assert ref is a  # same obj in memory