#[test]
fn vtable_string_substring_concat() {
    use crate::backend::vm::VM;
    use crate::mir::{MirModule, MirFunction, FunctionSignature, MirInstruction, EffectMask, BasicBlockId, ConstValue, MirType};
    std::env::set_var("NYASH_ABI_VTABLE", "1");

    // substring: "hello".substring(1,4) == "ell"
    let sig = FunctionSignature { name: "main".into(), params: vec![], return_type: MirType::String, effects: EffectMask::PURE };
    let mut f = MirFunction::new(sig, BasicBlockId::new(0));
    let bb = f.entry_block;
    let s = f.next_value_id(); f.get_block_mut(bb).unwrap().add_instruction(MirInstruction::Const { dst: s, value: ConstValue::String("hello".into()) });
    let sb = f.next_value_id(); f.get_block_mut(bb).unwrap().add_instruction(MirInstruction::NewBox { dst: sb, box_type: "StringBox".into(), args: vec![s] });
    let i1 = f.next_value_id(); f.get_block_mut(bb).unwrap().add_instruction(MirInstruction::Const { dst: i1, value: ConstValue::Integer(1) });
    let i4 = f.next_value_id(); f.get_block_mut(bb).unwrap().add_instruction(MirInstruction::Const { dst: i4, value: ConstValue::Integer(4) });
    let sub = f.next_value_id();
    f.get_block_mut(bb).unwrap().add_instruction(MirInstruction::BoxCall { dst: Some(sub), box_val: sb, method: "substring".into(), args: vec![i1, i4], method_id: None, effects: EffectMask::PURE });
    f.get_block_mut(bb).unwrap().add_instruction(MirInstruction::Return { value: Some(sub) });
    let mut m = MirModule::new("str_sub".into()); m.add_function(f);
    let mut vm = VM::new();
    let out = vm.execute_module(&m).expect("vm exec");
    assert_eq!(out.to_string_box().value, "ell");

    // concat: "ab".concat("cd") == "abcd"
    let sig2 = FunctionSignature { name: "main".into(), params: vec![], return_type: MirType::String, effects: EffectMask::PURE };
    let mut f2 = MirFunction::new(sig2, BasicBlockId::new(0));
    let bb2 = f2.entry_block;
    let a = f2.next_value_id(); f2.get_block_mut(bb2).unwrap().add_instruction(MirInstruction::Const { dst: a, value: ConstValue::String("ab".into()) });
    let ab = f2.next_value_id(); f2.get_block_mut(bb2).unwrap().add_instruction(MirInstruction::NewBox { dst: ab, box_type: "StringBox".into(), args: vec![a] });
    let c = f2.next_value_id(); f2.get_block_mut(bb2).unwrap().add_instruction(MirInstruction::Const { dst: c, value: ConstValue::String("cd".into()) });
    let joined = f2.next_value_id();
    f2.get_block_mut(bb2).unwrap().add_instruction(MirInstruction::BoxCall { dst: Some(joined), box_val: ab, method: "concat".into(), args: vec![c], method_id: None, effects: EffectMask::PURE });
    f2.get_block_mut(bb2).unwrap().add_instruction(MirInstruction::Return { value: Some(joined) });
    let mut m2 = MirModule::new("str_concat".into()); m2.add_function(f2);
    let mut vm2 = VM::new();
    let out2 = vm2.execute_module(&m2).expect("vm exec");
    assert_eq!(out2.to_string_box().value, "abcd");
}