Read content file outside of eval block

[atoomic]

spec_helper is sneaking in some content
from a file to a namespace.

But it's not required to read the file
inside the quoted eval.

Reading it earlier provides the advantage
of building the OP tree for it, so
we can use Test::Mockfile without impacting
this test module.

It also reduces the length of the string eval
and optimize it and make it easier to maintain
at the same time.