chore: improve snapshot readability

Author: gengjiawen

parser/ast_tree_test.rs

@@ -4,13 +4,13 @@ mod tests {
     use insta::*;
 
     pub fn test_ast_tree(name: &str, input: &str) {
-        let let_ast = match parse(input) {
+        let ast = match parse(input) {
             Ok(node) => {
                 serde_json::to_string_pretty(&node).unwrap()
             }
             Err(e) => format!("parse error: {}", e[0])
         };
-        assert_snapshot!(name, let_ast);
+        assert_snapshot!(name, ast, input);
     }
 
     #[test]