assert_equal "", @response.body
assert_equal "new_value", UserPreference.find([user.id, "key"]).v
assert_equal "value", UserPreference.find([user.id, "new_key"]).v
assert_equal "", @response.body
assert_equal "new_value", UserPreference.find([user.id, "key"]).v
assert_equal "value", UserPreference.find([user.id, "new_key"]).v