Add unit tests for calculator

CalculatorLibrary/test_calculator.py

@@ -0,0 +1,14 @@
+"""
+Unit tests for the calculator library
+"""
+
+import calculator
+
+
+class TestCalculator:
+
+    def test_addition(self):
+        assert 4 == calculator.add(2, 2)
+
+    def test_subtract(self):
+        assert 2 == calculator.subtract(4, 2)