[core] add test for json parser (#15297)

this should fail, but isnt

---------

Co-authored-by: Nuno Campos <nuno@langchain.dev>

libs/core/tests/unit_tests/output_parsers/test_json.py

@@ -487,3 +487,9 @@ async def test_partial_text_json_output_parser_diff_async() -> None:
     chain = input_iter | SimpleJsonOutputParser(diff=True)
 
     assert [p async for p in chain.astream(None)] == EXPECTED_STREAMED_JSON_DIFF
+
+
+def test_raises_error() -> None:
+    parser = SimpleJsonOutputParser()
+    with pytest.raises(Exception):
+        parser.invoke("hi")