You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: tests.rs
    path of file: ./repos/boa/core/parser/src/parser/expression/primary/function_expression
    
    the code of the file until where you have to start completion: use crate::parser::tests::check_script_parser;
use boa_ast::{
    declaration::{LexicalDeclaration, Variable},
    expression::literal::Literal,
    function::{FormalParameterList, Function, FunctionBody},
    statement::Return,
    Declaration, Statement, StatementListItem,
};
use boa_interner::Interner;
use boa_macros::utf16;

/// Checks async expression parsing.
#[test]
fn check_function_expression() {
    let interner = &mut Interner::default();
    let add = interner.get_or_intern_static("add", utf16!("add"));
    check_script_parser(
        "const add = function() {
            return 1;
        };
        ",
        vec![Declaration::Lexical(LexicalDeclaration::Const(
            vec![Variable::from_identifier(
                add.into(),
             
    
fn check_nested_function_expression() {
    let interner = &mut Interner::default();
    let a = interner.get_or_intern_static("a", utf16!("a"));
    let b = interner.get_or_intern_static("b", utf16!("b"));
    check_script_parser(
        "const a = function() {
            const b = function() {
                return 1;
            };
        };
        ",
        vec![Declaration::Lexical(LexicalDeclaration::Const(
            vec![Variable::from_identifier(
                a.into(),
                Some(
                    Function::new(
                        Some(a.into()),
                        FormalParameterList::default(),
                        FunctionBody::new(
                            vec![Declaration::Lexical(LexicalDeclaration::Const(
                                vec![Variable::from_identifier(
                                    b.into(),
                                    Some(
                                        Function::new(
                                            Some(b.into()),
                                            FormalParameterList::default(),
                                            FunctionBody::new(
                                                vec![StatementListItem::Statement(
                                                    Statement::Return(Return::new(Some(
                                                        Literal::from(1).into(),
                                                    ))),
                                                )]
                                                .into(),
                                            ),
                                        )
                                        .into(),
                                    ),
                                )]
                                .try_into()
                                .unwrap(),
                            ))
                            .into()]
                            .into(),
                        ),
                    )
                    .into(),
                ),
            )]
            .try_into()
            .unwrap(),
        ))
        .into()],
        interner,
    );
}