standardize json parsing (#5168)

Co-authored-by: Dev 2049 <dev.dev2049@gmail.com>

tests/unit_tests/output_parsers/test_json.py

@@ -0,0 +1,81 @@
+import pytest
+
+from langchain.output_parsers.json import parse_json_markdown
+
+GOOD_JSON = """```json
+{
+    "foo": "bar"
+}
+```"""
+
+JSON_WITH_NEW_LINES = """
+
+```json
+{
+    "foo": "bar"
+}
+```
+
+"""
+
+JSON_WITH_NEW_LINES_INSIDE = """```json
+{
+
+    "foo": "bar"
+
+}
+```"""
+
+JSON_WITH_NEW_LINES_EVERYWHERE = """
+
+```json
+
+{
+
+    "foo": "bar"
+
+}
+
+```
+
+"""
+
+TICKS_WITH_NEW_LINES_EVERYWHERE = """
+
+```
+
+{
+
+    "foo": "bar"
+
+}
+
+```
+
+"""
+
+NO_TICKS = """{
+    "foo": "bar"
+}"""
+
+NO_TICKS_WHITE_SPACE = """
+{
+    "foo": "bar"
+}
+"""
+
+TEST_CASES = [
+    GOOD_JSON,
+    JSON_WITH_NEW_LINES,
+    JSON_WITH_NEW_LINES_INSIDE,
+    JSON_WITH_NEW_LINES_EVERYWHERE,
+    TICKS_WITH_NEW_LINES_EVERYWHERE,
+    NO_TICKS,
+    NO_TICKS_WHITE_SPACE,
+]
+
+
+@pytest.mark.parametrize("json_string", TEST_CASES)
+def test_parse_json(json_string: str) -> None:
+    parsed = parse_json_markdown(json_string)
+    assert parsed == {"foo": "bar"}