Update assertFn to use custom error message

Author: rayokota

src/jsonata/functions.py

@@ -1836,7 +1836,8 @@ def each(obj: Optional[Mapping], func: Any) -> Optional[list]:
     #     
     @staticmethod
     def error(message: Optional[str]) -> NoReturn:
-        raise jexception.JException("D3137", -1, message if message is not None else "$error() function evaluated")
+        raise jexception.JException("D3137", -1,
+                                    message if message is not None else "$error() function evaluated")
 
     #
     #
@@ -1851,8 +1852,8 @@ def assert_fn(condition: Optional[bool], message: Optional[str]) -> None:
             raise jexception.JException("T0410", -1)
 
         if not condition:
-            raise jexception.JException("D3141", -1, "$assert() statement failed")
-            #                message: message || "$assert() statement failed"
+            raise jexception.JException("D3141", -1,
+                                        message if message is not None else "$assert() statement failed")
 
     #
     #

src/jsonata/jexception.py

@@ -105,6 +105,9 @@ def msg(error: str, location: int, arg1: Optional[Any], arg2: Optional[Any], det
 
         formatted = message
 
+        if formatted == "{{{message}}}":
+            return str(arg1)
+
         # Replace any {{var}} with format "{}"
         formatted = re.sub("\\{\\{\\w+\\}\\}", "{}", formatted)
 

tests/array_test.py

@@ -1,4 +1,5 @@
 import jsonata
+import pytest
 
 
 class TestArray:
@@ -31,3 +32,9 @@ def test_wildcard_filter(self):
 
         expression2 = jsonata.Jsonata("**[value.Product = 'Product1']")
         assert expression2.evaluate(data) == value1
+
+    def test_assert_custom_message(self):
+        expr = jsonata.Jsonata("$assert(false, 'custom error')")
+        with pytest.raises(jsonata.JException) as exc_info:
+            expr.evaluate(None)
+        assert "custom error" in str(exc_info.value)