test_endofcode_behavior()¶

def test_endofcode_behavior(
    pre: Alloc,
    state_test: StateTestFiller,
) -> None:
    """
    Test DUPN when the immediate byte is beyond the end of code.

    Per EIP-8024, code[pc + 1] evaluates to 0 if beyond the end of the code,
    matching PUSH behavior. With immediate = 0, decode_single(0) = 145, so
    DUPN duplicates the 145th stack item.

    This test verifies the transaction succeeds (doesn't revert) when DUPN
    is the last byte of the code with no immediate byte following it.
    """
    sender = pre.fund_eoa()

    # decode_single(0) = 145, which duplicates the 145th item from top
    # We need 145 items on the stack for this to succeed
    stack_height = 145
    marker_value = 0x42

    # Build code: store marker, push enough items, then DUPN (no immediate)
    code = Bytecode()
    code += Op.SSTORE(0, marker_value)  # Store marker

    # Push 145 items to stack so DUPN with implicit imm=0 succeeds
    for i in range(stack_height):
        code += Op.PUSH1(i % 256)

    # Add just the DUPN opcode without immediate byte
    # After DUPN, pc += 2 goes beyond code, causing implicit STOP
    code += Op.DUPN  # no immediate

    contract_address = pre.deploy_contract(code=code)

    tx = Transaction(to=contract_address, sender=sender)

    # If tx succeeds, storage[0] = marker_value
    # Bad implementation would revert and have empty storage
    post = {contract_address: Account(storage={0: marker_value})}

    state_test(pre=pre, post=post, tx=tx)