Fixture error in Minitest: table has no column named X - ruby-on-rails-4

Question

I'm hitting a wall trying to set up tests for my user_tests model.
The error (one example of many) I get when running the tests (minitest):
ERROR["test_should_get_new", Admin::TestConfigsControllerTest, 2016-01-07 13:04:02 +0100]
test_should_get_new#Admin::TestConfigsControllerTest (1452168242.12s)
ActiveRecord::Fixture::FixtureError:
ActiveRecord::Fixture::FixtureError: table "user_tests" has no column named "user".
It's correct that there is no column named user, but there is a user_id and in other fixtures, this is working correctly. What is wrong with my setup that for this model the columns can't be found?
The fixture user_tests.yml:
user_test_one:
started: false
started_at:
finished: false
finished_at:
invited: true
invited_at: <%= Time.zone.now %>
user: michael
test_config: test_config_one
test_result:
test_result_type:
user_test_two:
started: false
started_at:
finished: false
finished_at:
test_result:
test_result_type:
invited: false
invited_at:
user: michael
test_config: test_config_two
test_result:
test_result_type:
Here both user, test_config and test_result should point to columns user_id, test_config_id and test_result_id. All give the same type of errors.
It works fine for users.yml where both company and user_group are links to other tables (shout out to Michael Hartle for the excellent Ruby on Rails Tutorial):
michael:
first_name: Michael
last_name: Example
email: michael#example.com
password_digest: <%= User.digest('password') %>
admin: true
activated: true
activated_at: <%= Time.zone.now %>
company: my-company
user_group: my-company-groep
archer:
first_name: Sterling
last_name: Archer
email: duchess#example.gov
password_digest: <%= User.digest('password') %>
activated: true
activated_at: <%= Time.zone.now %>
company: my-company
user_group: my-company-groep
The first lines from the users_test.rb model:
class UserTest < ActiveRecord::Base
belongs_to :user, required: true
belongs_to :test_config, required: true
belongs_to :test_result, polymorphic: true
attr_accessor :step, :send_invitation
Can't find anything wrong with the database either. Here's a screenshot of both the users and user_tests tables in SQLite:
Any thoughts?
Update: It must have something to do with the test not finding the model user_test.rb for this fixture (user_tests.yml). I can convert the columns user and test_config to include _id but then an error occurs that the created_at and updated_at columns may not be nil (ActiveRecord::StatementInvalid: SQLite3::ConstraintException: NOT NULL constraint failed: user_tests.created_at). Those should be handled by Rails, but aren't. Why?
user_test_one:
started: false
started_at:
finished: false
finished_at:
invited: true
invited_at: <%= Time.zone.now %>
test_config_id: 1
user_id: 1
created_at: <%= Time.zone.now %>
updated_at: <%= Time.zone.now %>
Update 2: I've got a strong suspicion the problem is caused by including "Test" in the model/table name

Answer 1

Renaming the table and all corresponding code from user_test (and all variants) to user_survey solved the problem.