Minitest 6 will not allow assert_equal to compare for equality
with nil and minitest 5 has already started warning about it.
That's fine if you're comparing with a nil constant, but if you're
comparing with an expression that is sometimes nil and sometimes
not nil it's an absolute pain in the rear end.
For some tests, the existance of an 'en' language is assumed by
the database structure (not null default 'en'::character varying) so
this can be created in a setup block.
Rather than passing around record ids explicitly, we can use the
model relations and pass around the models. This makes reading the
tests slightly simpler to read.
Implement our own matching algorithm rather than trying to
patch the http_accept_language one and make sure everything is
using it in a consistent way.
Fixes#1125
