feat(content): function signatures + test cases

backend/data/questions/calculate-digit-sum-of-a-string.yaml

@@ -8,6 +8,26 @@ categories:
 patterns:
   - sliding-window
 
+function_signature: "def digit_sum(s: str, k: int) -> str:"
+
+test_cases:
+  visible:
+    - input: { s: "11111222223", k: 3 }
+      expected: "135"
+    - input: { s: "00000000", k: 3 }
+      expected: "000"
+  hidden:
+    - input: { s: "1", k: 2 }
+      expected: "1"
+    - input: { s: "123", k: 3 }
+      expected: "123"
+    - input: { s: "999", k: 2 }
+      expected: "27"
+    - input: { s: "12345", k: 2 }
+      expected: "39"
+    - input: { s: "111111", k: 2 }
+      expected: "6"
+
 description: |
   You are given a string `s` consisting of digits and an integer `k`.