`require_ok "open"` fails

require_ok "open" fails by trying to use the open operator.

This can be resolved by replacing

    # Try to determine if we've been given a module name or file.
    # Module names must be barewords, files not.
    $module = qq['$module'] unless _is_module_name($module);
 
    my $code = <<REQUIRE;
package $pack;
require $module;
1;
REQUIRE

with

    # Try to determine if we've been given a module name or file.
    # Module names must be barewords, files not.
    my $code = ( _is_module_name($module)
        ? "require '$module'"
        : "use $module ()"
    );
 
    $code = <<REQUIRE;
package $pack;
$code;
1;
REQUIRE

Start at the implementation of require_ok and reproduce the failure with the module name "open". Add regression coverage for this case, then run the relevant Perl test suite; done means require_ok "open" succeeds without invoking the open operator.