diff --git a/src/calculator.py b/src/calculator.py
index 77e1607..570966c 100644
--- a/src/calculator.py
+++ b/src/calculator.py
@@ -2,3 +2,7 @@
 def add(a: float, b: float) -> float:
     """Add two numbers and return the result."""
     return a + b
+
+def diff(a: float, b: float) -> float:
+    """Add two numbers and return the result."""
+    return a - b
diff --git a/tests/test_calculator.py b/tests/test_calculator.py
index dabf164..5bd2bb0 100644
--- a/tests/test_calculator.py
+++ b/tests/test_calculator.py
@@ -1,12 +1,16 @@
 """Unit tests for the calculator module."""
 
-from src.calculator import add
+from src.calculator import add, diff
 
 
 def test_add_positive_numbers() -> None:
     """Test adding two positive numbers."""
     assert add(2, 3) == 5
 
+def test_diff_positive_numbers() -> None:
+    """Test adding two positive numbers."""
+    assert diff(3, 1) == 2
+
 
 def test_add_negative_numbers() -> None:
     """Test adding two negative numbers."""