diff --git a/StringCalculator.py b/StringCalculator.py
new file mode 100644
index 0000000000000000000000000000000000000000..f9a7682047dc083481c1547f9a9ef1d5bed8a72c
--- /dev/null
+++ b/StringCalculator.py
@@ -0,0 +1,29 @@
+from abc import ABC, abstractmethod
+import unittest
+
+class IStringCalculator(ABC):
+    @abstractmethod
+    def add(self, numbers: str) -> int:
+        pass
+
+class StringCalculator(IStringCalculator):
+    def add(self, numbers: str) -> int:
+        if not numbers:
+            return 0
+        return sum(map(int, numbers.split(',')))
+
+class TestStringCalculator(unittest.TestCase):
+    def setUp(self):
+        self.calculator = StringCalculator()
+    
+    def test_empty_string(self):
+        self.assertEqual(self.calculator.add(""), 0)
+    
+    def test_single_number(self):
+        self.assertEqual(self.calculator.add("1"), 1)
+    
+    def test_two_numbers(self):
+        self.assertEqual(self.calculator.add("1,2"), 3)
+
+if __name__ == "__main__":
+    unittest.main()
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