Made test case to replicate #396.

tests/test_source.py

@@ -0,0 +1,15 @@
+import montepy
+from montepy.data_inputs.data_parser import parse_data
+from montepy.input_parser.block_type import BlockType
+from montepy.input_parser.mcnp_input import Input
+
+import pytest
+
+
+@pytest.mark.parametrize(
+    "line", ["sdef  cel=d1 erg=d2 pos=fcel d3 ext=fcel d4 axs=0 0 1 rad=d5"]
+)
+def test_source_parse_and_parrot(line):
+    input = Input([line], BlockType.DATA)
+    data = parse_data(input)
+    assert data._tree.format() == line