Bug 18286: Test::DBIx::Class connection/schema is shadowed by a cached connection...

Bug 18286: Test::DBIx::Class connection/schema is shadowed by a cached connection/schema

If Koha::Database->schema gets called before

    use Test::DBIx::Class

The DB connection from $KOHA_CONF is cached.

This happens most of the time because when C4::Context and friends are loaded
(in compile-time?), they already access the DB.

After Test::DBIx::Class is instantiated and hooks put in place to overload
Koha::Schema connection, those hooks are never called due to getting the old
connection from cache.

This feature introduces a test case to replicate the behaviour and shows how
flushing the connection cache solves the problem.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>