diff --git a/calculator.py b/calculator.py
new file mode 100644
index 0000000..b29111d
--- /dev/null
+++ b/calculator.py
@@ -0,0 +1,37 @@
+import argparse
+
+def add(x, y):
+  """Adds two numbers together."""
+  return x + y
+
+def subtract(x, y):
+  """Subtracts two numbers."""
+  return x - y
+
+def multiply(x, y):
+  """Multiplies two numbers."""
+  return x * y
+
+def divide(x, y):
+  """Divides two numbers."""
+  if y == 0:
+    raise ValueError("Cannot divide by zero.")
+  return x / y
+
+if __name__ == "__main__":
+  parser = argparse.ArgumentParser(description="A simple command-line calculator.")
+  parser.add_argument("x", type=float, help="The first number.")
+  parser.add_argument("operation", choices=["+", "-", "*", "/"], help="The operation to perform.")
+  parser.add_argument("y", type=float, help="The second number.")
+  args = parser.parse_args()
+
+  if args.operation == "+":
+    result = add(args.x, args.y)
+  elif args.operation == "-":
+    result = subtract(args.x, args.y)
+  elif args.operation == "*":
+    result = multiply(args.x, args.y)
+  elif args.operation == "/":
+    result = divide(args.x, args.y)
+
+  print(f"Result: {result}")
diff --git a/test_calculator.py b/test_calculator.py
new file mode 100644
index 0000000..3c556a1
--- /dev/null
+++ b/test_calculator.py
@@ -0,0 +1,29 @@
+import unittest
+from calculator import add, subtract, multiply, divide
+
+class TestCalculator(unittest.TestCase):
+
+    def test_add(self):
+        self.assertEqual(add(2, 3), 5)
+        self.assertEqual(add(-1, 1), 0)
+        self.assertEqual(add(-1, -1), -2)
+
+    def test_subtract(self):
+        self.assertEqual(subtract(3, 2), 1)
+        self.assertEqual(subtract(-1, 1), -2)
+        self.assertEqual(subtract(-1, -1), 0)
+
+    def test_multiply(self):
+        self.assertEqual(multiply(2, 3), 6)
+        self.assertEqual(multiply(-1, 1), -1)
+        self.assertEqual(multiply(-1, -1), 1)
+
+    def test_divide(self):
+        self.assertEqual(divide(6, 3), 2)
+        self.assertEqual(divide(-1, 1), -1)
+        self.assertEqual(divide(-1, -1), 1)
+        with self.assertRaises(ValueError):
+            divide(1, 0)
+
+if __name__ == '__main__':
+    unittest.main()