[Rails] Minitest のエラーの見方について

前提・実現したいこと

Railsのチュートリアルを見ながら、勉強中の初心者です。

初歩的な質問かもしれませんが、Rails test で、単体テストを行った際、テストに記載していない内容のエラーが発生し、エラーの原因がわからず困ってます。
どのソースが実行されているのか（どのソースでエラーになっているのか）確認する方法を教えて欲しいです。

発生している問題・エラーメッセージ

rails test test/controllers/users_controller_test.rb 
を実行したときに、以下のエラーが発生してます。

Running via Spring preloader in process 759
Run options: --seed 14248

# Running:

E

Error:
UsersControllerTest#test_should_get_index:
ActiveRecord::ValueTooLong: Mysql2::Error: Data too long for column 'phase_id' at row 1: INSERT INTO `testphases` (`created_at`, `updated_at`, `phase_id`) VALUES ('2018-01-07 09:51:16', '2018-01-07 09:51:16', '298486374')

Traceback (most recent call last):
    27: from -e:1:in `<main>'
    26: from /Users/shara/.rbenv/versions/2.5.0/lib/ruby/2.5.0/rubygems/core_ext/kernel_require.rb:59:in `require'
    25: from /Users/shara/.rbenv/versions/2.5.0/lib/ruby/2.5.0/rubygems/core_ext/kernel_require.rb:59:in `require'
    24: from /Users/shara/.rbenv/versions/2.5.0/lib/ruby/gems/2.5.0/gems/spring-2.0.2/lib/spring/application/boot.rb:19:in `<top (required)>'
    23: from /Users/shara/.rbenv/versions/2.5.0/lib/ruby/gems/2.5.0/gems/spring-2.0.2/lib/spring/application.rb:135:in `run'
    22: from /Users/shara/.rbenv/versions/2.5.0/lib/ruby/gems/2.5.0/gems/spring-2.0.2/lib/spring/application.rb:135:in `loop'
    21: from /Users/shara/.rbenv/versions/2.5.0/lib/ruby/gems/2.5.0/gems/spring-2.0.2/lib/spring/application.rb:141:in `block in run'
    20: from /Users/shara/.rbenv/versions/2.5.0/lib/ruby/gems/2.5.0/gems/spring-2.0.2/lib/spring/application.rb:171:in `serve'
    19: from /Users/shara/.rbenv/versions/2.5.0/lib/ruby/gems/2.5.0/gems/spring-2.0.2/lib/spring/application.rb:171:in `fork'
    18: from /Users/shara/.rbenv/versions/2.5.0/lib/ruby/gems/2.5.0/gems/minitest-5.11.1/lib/minitest.rb:63:in `block in autorun'
    17: from /Users/shara/.rbenv/versions/2.5.0/lib/ruby/gems/2.5.0/gems/minitest-5.11.1/lib/minitest.rb:136:in `run'
    16: from /Users/shara/.rbenv/versions/2.5.0/lib/ruby/gems/2.5.0/gems/minitest-5.11.1/lib/minitest.rb:159:in `__run'
    15: from /Users/shara/.rbenv/versions/2.5.0/lib/ruby/gems/2.5.0/gems/minitest-5.11.1/lib/minitest.rb:159:in `map'
    14: from /Users/shara/.rbenv/versions/2.5.0/lib/ruby/gems/2.5.0/gems/minitest-5.11.1/lib/minitest.rb:159:in `block in __run'
    13: from /Users/shara/.rbenv/versions/2.5.0/lib/ruby/gems/2.5.0/gems/railties-5.1.4/lib/rails/test_unit/line_filtering.rb:9:in `run'
    12: from /Users/shara/.rbenv/versions/2.5.0/lib/ruby/gems/2.5.0/gems/minitest-5.11.1/lib/minitest.rb:319:in `run'
    11: from /Users/shara/.rbenv/versions/2.5.0/lib/ruby/gems/2.5.0/gems/minitest-5.11.1/lib/minitest.rb:347:in `with_info_handler'
    10: from /Users/shara/.rbenv/versions/2.5.0/lib/ruby/gems/2.5.0/gems/minitest-5.11.1/lib/minitest.rb:360:in `on_signal'
     9: from /Users/shara/.rbenv/versions/2.5.0/lib/ruby/gems/2.5.0/gems/minitest-5.11.1/lib/minitest.rb:320:in `block in run'
     8: from /Users/shara/.rbenv/versions/2.5.0/lib/ruby/gems/2.5.0/gems/minitest-5.11.1/lib/minitest.rb:320:in `each'
     7: from /Users/shara/.rbenv/versions/2.5.0/lib/ruby/gems/2.5.0/gems/minitest-5.11.1/lib/minitest.rb:321:in `block (2 levels) in run'
     6: from /Users/shara/.rbenv/versions/2.5.0/lib/ruby/gems/2.5.0/gems/minitest-5.11.1/lib/minitest.rb:334:in `run_one_method'
     5: from /Users/shara/.rbenv/versions/2.5.0/lib/ruby/gems/2.5.0/gems/minitest-5.11.1/lib/minitest.rb:785:in `record'
     4: from /Users/shara/.rbenv/versions/2.5.0/lib/ruby/gems/2.5.0/gems/minitest-5.11.1/lib/minitest.rb:785:in `each'
     3: from /Users/shara/.rbenv/versions/2.5.0/lib/ruby/gems/2.5.0/gems/minitest-5.11.1/lib/minitest.rb:786:in `block in record'
     2: from /Users/shara/.rbenv/versions/2.5.0/lib/ruby/gems/2.5.0/gems/railties-5.1.4/lib/rails/test_unit/reporter.rb:23:in `record'
     1: from /Users/shara/.rbenv/versions/2.5.0/lib/ruby/gems/2.5.0/gems/railties-5.1.4/lib/rails/test_unit/reporter.rb:70:in `format_rerun_snippet'
/Users/shara/.rbenv/versions/2.5.0/lib/ruby/gems/2.5.0/gems/railties-5.1.4/lib/rails/test_unit/reporter.rb:70:in `method': undefined method `test_should_get_index' for class `Minitest::Result' (NameError)

INSERTを発行するテストは行っていないにも関わらず、INSERTのエラーが発生しています。
テスト範囲を、test/controllers/users_controller_test.rb　で指定しており、このソース内には、CREATEのイベント発行は行っていません。

該当のソースコード

test/controllers/users_controller_test.rb

  1 require 'test_helper'
  2 
  3 class UsersControllerTest < ActionDispatch::IntegrationTest
  4   setup do
  5     @user = users(:one)
  6   end
  7 
  8   test "should get index" do
  9     get users_path
 10     assert_response :success                                                                                        
 11   end
 12 end

config/routes.rb

  1 Rails.application.routes.draw do                                                                                    
  2   resources :projects
  3   resources :testids
  4   get 'sessions/new'
  5 
  6     root   'static_pages#home'
  7     get    '/home',    to: 'static_pages#home'
  8     get    '/signup',  to: 'users#new'
  9     get    '/login',   to: 'sessions#new'
 10     post   '/login',   to: 'sessions#create'
 11     delete '/logout',  to: 'sessions#destroy'
 12 
 13     resources :users
 14 
 15   # For details on the DSL available within this file, see http://guides.rubyonrails.org/routing.html
 16 end

試したこと

1   8行目〜11行目をコメントアウトしてテストをすると、エラーは出ず、何も処理がされずに終了します。

Running via Spring preloader in process 815
Run options: --seed 48142

# Running:

Finished in 0.001560s, 0.0000 runs/s, 0.0000 assertions/s.
0 runs, 0 assertions, 0 failures, 0 errors, 0 skips

2   test/controllers 内の他のテストファイルをコメントアウトしても状況は変わりませんでした。

補足情報(言語/FW/ツール等のバージョンなど)

MacOSX 10.13.2 (High Sierra)
MySQL 5.7.19
Ruby 2.5.0p0 (2017-12-25 revision 61468) [x86_64-darwin17]
rails (5.1.4)
minitest (5.11.1, 5.10.3)