testing for unsuccessful require - mocking require ?

[Gabor Szabo]

I would like to test a module for unsuccessful "require" while the
required module is installed. That is I'd like ot test how my code would
work if Foo.pm was not present.

In the middle of a module I have code such as

eval {
   require Foo;
};
if ($@) {
   foo();
} else {
   my_own_foo();
}

I already installed Foo so I can test the behaviour of the code
with Foo. How can I test now the behaviour without Foo ?
Removing Foo.pm is not an option.

I have some ideas outlined below, but I'd like to get your recommendation.

The first solution was to reset @INC = (); so that require won't
find Foo. This seems to be good with one minor problem.
Just before require Foo; I have require Bar; and I'd like to
be able to  actually use Bar in the same code.


I thought of overriding the built in require function so it will
selectively either throw an error message or execute the core behaviour.
That is on Foo it will throw an error message while on the rest, including
Bar it will do the work.


According to the Cookbook (2nd) I cannot override require as of 5.8.1.

I am using 5.8.4 right now and tried
1) use ex::override
got:  require cannot be overridden because it doesn't have a prototype at
override.pl line 3


2) use Function::Override;
got: Cannot override the non-overridable builtin 'require'


3) rolled my own override using
use subs qw(require);
and the example code from perldoc -f require

This seems to be working.


So I am a bit confused for why 1 and 2 are not working while using my own
code does.


In general I'd like to get your opinion on how to mock unsuccessful
require.

thanks
   Gabor