add tests

Author: aman-coder03

tests/test_transformer.py

@@ -58,3 +58,24 @@ def test_simple_efficiency_known_values():
                                       *args),
         rating,
     )
+
+
+def test_simple_efficiency_zero_load_loss():
+
+    input_power = 1000.0
+    no_load_loss = 0.01
+    load_loss = 0.0
+    transformer_rating = 1000.0
+
+    result = transformer.simple_efficiency(
+        input_power=input_power,
+        no_load_loss=no_load_loss,
+        load_loss=load_loss,
+        transformer_rating=transformer_rating,
+    )
+
+    # for load_loss = 0, the model reduces to:
+    # P_out = P_in - L_no_load * P_nom
+    expected = input_power - no_load_loss * transformer_rating
+
+    assert_allclose(result, expected)