ruby on rails - What to stub, in order to test an ActiveRecord validates_uniqueness_of -

i have simplified model:

class site < activerecord::base   validates :primary_domain, uniqueness: true end 

and have test in minitest-spec:

describe "primary_domain"   "must unique"     site.create(primary_domain: "example.com")     s = site.new(primary_domain: "example.com")     s.wont_be valid?     s.errors.messages.keys.must_include :primary_domain   end end 

but requires few roundtrips database, find break concept of unit-test. there can stub exclude entire database-layer?

e.g. when using mocha:

describe "primary_domain"   "must unique"     site.stubs(:find_by).with(primary_domain: "example.com").returns([site.new])     s = site.new(primary_domain: "example.com")     s.wont_be valid?     s.errors.messages.keys.must_include :primary_domain   end end 

apparently uniqueness validator not use find_by, other check. there better candidate stub out here achieve same?