diff --git a/Feature6.py b/Feature6.py
new file mode 100644
index 0000000000000000000000000000000000000000..0f35297ebc07e1bd3d13bb70713f3ecbe5b9f33a
--- /dev/null
+++ b/Feature6.py
@@ -0,0 +1,94 @@
+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
+        
+        # Überprüfe, ob ein benutzerdefiniertes Trennzeichen angegeben ist
+        if numbers.startswith("//"):
+            delimiter_line_end = numbers.find("\n")
+            delimiter = numbers[2:delimiter_line_end]  # Extrahiere das Trennzeichen
+            numbers = numbers[delimiter_line_end + 1:]  # Entferne die erste Zeile mit dem Trennzeichen
+            
+        else:
+            delimiter = ','  # Standard-Trennzeichen ist Komma, wenn keine Zeile mit dem Trennzeichen vorhanden ist
+
+        # Ersetze alle Vorkommen des Trennzeichens und teile die Eingabe
+        numbers = numbers.replace("\n", delimiter)
+        nums = numbers.split(delimiter)
+        
+        # Filtere alle Zahlen, die größer als 1000 sind
+        nums = [int(num) for num in nums if int(num) <= 1000]
+        
+        # Prüfe auf negative Zahlen
+        negatives = [num for num in nums if num < 0]
+        
+        if negatives:
+            # Wenn negative Zahlen vorhanden sind, werfe eine Ausnahme
+            raise ValueError(f"Negatives not allowed: {', '.join(map(str, negatives))}")
+        
+        # Berechne die Summe der Zahlen, die <= 1000 sind
+        return sum(nums)
+
+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)
+    
+    def test_multiple_numbers(self):
+        self.assertEqual(self.calculator.add("1,2,3,4,5"), 15)
+    
+    def test_numbers_with_newline(self):
+        self.assertEqual(self.calculator.add("1\n2,3"), 6)
+    
+    def test_numbers_with_multiple_newlines(self):
+        self.assertEqual(self.calculator.add("1\n2\n3\n4\n5"), 15)
+    
+    def test_negative_number(self):
+        with self.assertRaises(ValueError) as context:
+            self.calculator.add("1,-2,3")
+        self.assertEqual(str(context.exception), "Negatives not allowed: -2")
+    
+    def test_multiple_negative_numbers(self):
+        with self.assertRaises(ValueError) as context:
+            self.calculator.add("1,-2,-3,4")
+        self.assertEqual(str(context.exception), "Negatives not allowed: -2, -3")
+    
+    def test_custom_delimiter(self):
+        self.assertEqual(self.calculator.add("//;\n1;2"), 3)
+    
+    def test_custom_delimiter_with_newline(self):
+        self.assertEqual(self.calculator.add("//;\n1;2\n3"), 6)
+    
+    def test_custom_delimiter_with_multiple_numbers(self):
+        self.assertEqual(self.calculator.add("//|\n1|2|3|4"), 10)
+    
+    def test_numbers_greater_than_1000(self):
+        self.assertEqual(self.calculator.add("2,1001"), 2)
+    
+    def test_numbers_greater_than_1000_with_custom_delimiter(self):
+        self.assertEqual(self.calculator.add("//;\n2;1001"), 2)
+    
+    def test_long_delimiter(self):
+        self.assertEqual(self.calculator.add("//[***]\n1***2***3"), 6)
+    
+    def test_long_delimiter_with_multiple_numbers(self):
+        self.assertEqual(self.calculator.add("//[---]\n1---2---3---4"), 10)
+
+if __name__ == "__main__":
+    unittest.main()
\ No newline at end of file