syntax_data: {"ast_node_type":"other","tokens":[{"end":60,"kind":"keyword","start":0,"text":"assert_eq!(sf.lookup_line(RelativeBytePos(1)),"}]}
source_snippet:     assert_eq!(sf.lookup_line(RelativeBytePos(1)), Some(0));
context_before:     assert_eq!(sf.lookup_line(RelativeBytePos(0)), Some(0));