Running unit tests on controllers fails before started - ruby-on-rails

Question

Just started to learn Ruby and Rails and currently have I created a controller to authenticate a user and provide a token. It works perfect doing monkey testing (clicking around and postman), but when doing testing with this command:
rails test
will even this test fail:
require 'test_helper'
class UserControllerTest < ActionDispatch::IntegrationTest
test "should be true" do
assert true
end
end
It will output this in the terminal:
Error:
UserControllerTest#test_should_be_true:
ActiveRecord::StatementInvalid: SQLite3::ConstraintException: NOT
NULL constraint failed: users.email: INSERT INTO "users" ("created_at",
"updated_at", "id") VALUES ('2017-03-18 11:11:35.973444', '2017-03-18 11:11:35.973444', 980190962)
Can't see what the problem should be. Because if I try to create a unit test inside the a ActiveSupport:TestCase will it fail with same output.
Can anyone tell me why it does this?
Obs!
If you need more information about the user controller just post a comment. Thanks.
Edit
In my applicationcontroller have this code:
class ApplicationController < ActionController::Base
require 'json_web_token'
protect_from_forgery with: :exception
protected
def authenticate_request!
if !payload || !JsonWebToken.valid_payload(payload.first)
return invalid_authentication
end
load_current_user!
invalid_authentication unless #current_user
end
def invalid_authentication
render json: { error: 'Invalid Request'}, status: :unauthorized
end
private
def payload
auth_header = request.headers['Authorization']
token = auth_header.split(' ').last
JsonWebToken.decode(token)
rescue
nil
end
def load_current_user!
#current_user = User.find_by(id: payload[0]['user_id'])
end
end
My test settings under config/environments/test.rb
Rails.application.configure do
config.cache_classes = true
config.eager_load = false
config.public_file_server.enabled = true
config.public_file_server.headers = {
'Cache-Control' => 'public, max-age=3600'
}
config.consider_all_requests_local = true
config.action_controller.perform_caching = false
config.action_dispatch.show_exceptions = false
config.action_controller.allow_forgery_protection = false
config.action_mailer.perform_caching = false
config.action_mailer.delivery_method = :test
config.active_support.deprecation = :stderr
config.action_controller.allow_forgery_protection = false
end

Answer 1

The problem is probably in your test/fixtures/users.yml. There are two users without attributes:
one: {}
# column: value
#
two: {}
# column: value
When minitest starts it attempts to create two users with empty fields and it violates not null constraint for email. Try to either remove these lines or populate them with correct values