trap is used in many tests to set actions to perform on cleanup.

IMHO, trap should be registered in this order:

cleanup_test_XX()
{
    undo_something
}

test_XX()
{
    trap cleanup_test_XX EXIT
    do_something
    ...
}

Currently many tests do not respect this template.
Among those, some:

• register the trap after do_something();
• explicitly call cleanup_test_XX() at the end of the test;
• call trap 0 at the start of cleanup_test_XX() (this one may be controversial, I believe the test harness should provide, and probably already provides, trap isolation between tests).