fix(checks): accept parsed string JSON values

libs/giskard-checks/src/giskard/checks/builtin/json_valid.py

@@ -114,7 +114,11 @@ async def run(self, trace: TraceType) -> CheckResult:
     @staticmethod
     def _parse_json(value: Any) -> Any:
         if isinstance(value, str):
-            return json.loads(value)
+            if value.strip() == "":
+                return json.loads(value)
+            if JsonValid._looks_like_serialized_json(value):
+                return json.loads(value)
+            return value
 
         try:
             json.dumps(value)
@@ -123,6 +127,27 @@ def _parse_json(value: Any) -> Any:
 
         return value
 
+    @staticmethod
+    def _looks_like_serialized_json(value: str) -> bool:
+        stripped = value.strip()
+        if not stripped:
+            return False
+
+        if stripped.startswith(("{", "[", '"')):
+            return True
+
+        if stripped in ("true", "false", "null"):
+            return True
+
+        if (stripped[:1].isdigit() or stripped.startswith("-")) and "_" not in stripped:
+            try:
+                parsed = json.loads(stripped)
+            except json.JSONDecodeError:
+                return False
+            return isinstance(parsed, int | float)
+
+        return False
+
     @staticmethod
     def _validate_schema_definition(schema: dict[str, Any]) -> None:
         validator_for(schema).check_schema(schema)

libs/giskard-checks/tests/builtin/test_json_valid.py

@@ -18,6 +18,12 @@
         ("null", None),
         ("true", True),
         ("42", 42),
+        ("hello", "hello"),
+        ("truth", "truth"),
+        ("falsehood", "falsehood"),
+        ("nullify", "nullify"),
+        ("123-apple", "123-apple"),
+        ("-infinity", "-infinity"),
     ],
 )
 async def test_valid_json_output_passes(outputs: Any, expected_parsed: Any) -> None:
@@ -37,6 +43,7 @@ async def test_valid_json_output_passes(outputs: Any, expected_parsed: Any) -> N
     [
         '{"name": "Alice"',
         "",
+        "   ",
     ],
 )
 async def test_invalid_json_string_fails(outputs: str) -> None:
@@ -83,6 +90,7 @@ async def test_nested_jsonpath_extraction() -> None:
         ),
         ({"type": "integer"}, 42, 42),
         ({"type": "string", "minLength": 3, "maxLength": 7}, '"hello"', "hello"),
+        ({"type": "string", "minLength": 3, "maxLength": 7}, "hello", "hello"),
     ],
 )
 async def test_schema_validation_passes(