add calculator

calculator/tests.py

@@ -0,0 +1,47 @@
+import unittest
+from pkg.calculator import Calculator
+
+
+class TestCalculator(unittest.TestCase):
+    def setUp(self):
+        self.calculator = Calculator()
+
+    def test_addition(self):
+        result = self.calculator.evaluate("3 + 5")
+        self.assertEqual(result, 8)
+
+    def test_subtraction(self):
+        result = self.calculator.evaluate("10 - 4")
+        self.assertEqual(result, 6)
+
+    def test_multiplication(self):
+        result = self.calculator.evaluate("3 * 4")
+        self.assertEqual(result, 12)
+
+    def test_division(self):
+        result = self.calculator.evaluate("10 / 2")
+        self.assertEqual(result, 5)
+
+    def test_nested_expression(self):
+        result = self.calculator.evaluate("3 * 4 + 5")
+        self.assertEqual(result, 17)
+
+    def test_complex_expression(self):
+        result = self.calculator.evaluate("2 * 3 - 8 / 2 + 5")
+        self.assertEqual(result, 7)
+
+    def test_empty_expression(self):
+        result = self.calculator.evaluate("")
+        self.assertIsNone(result)
+
+    def test_invalid_operator(self):
+        with self.assertRaises(ValueError):
+            self.calculator.evaluate("$ 3 5")
+
+    def test_not_enough_operands(self):
+        with self.assertRaises(ValueError):
+            self.calculator.evaluate("+ 3")
+
+
+if __name__ == "__main__":
+    unittest.main()