syntax_data: {"ast_node_type":"other","tokens":[{"end":30,"kind":"keyword","start":0,"text":"sf.start_pos"}]}
source_snippet:     sf.start_pos = BytePos(3);
context_before:     .unwrap();
context_after:     assert_eq!(sf.lines(), &[RelativeBytePos(0), RelativeBytePos(14), RelativeBytePos(25)]);