RoR: Test not running all assertions

I'm working through the Ruby on Rails Tutorial and encountering an unusual testing issue.

In brief, the command 'bundle exec rake test' is not running all the 'assertions' every time which results in 'errors' being produced.

1) When I first issue the command, I get the following result:

$ bundle exec rake test

Run options: --seed 37842

Running:

E........................E....E...

Finished in 1.076112s, 31.5952 runs/s, 123.5931 assertions/s.

1) Error: UsersIndexTest#test_index_as_admin_including_pagination_and_delete_links: AbstractController::ActionNotFound: The action 'destroy' could not be found for UsersController test/integration/users_index_test.rb:21:in block (2 levels) in <class:UsersIndexTest>' test/integration/users_index_test.rb:20:inblock in '

2) Error: UsersControllerTest#test_should_redirect_destroy_when_logged_in_as_a_non-admin: AbstractController::ActionNotFound: The action 'destroy' could not be found for UsersController test/controllers/users_controller_test.rb:57:in block (2 levels) in <class:UsersControllerTest>' test/controllers/users_controller_test.rb:56:inblock in '

3) Error: UsersControllerTest#test_should_redirect_destroy_when_not_logged_in: AbstractController::ActionNotFound: The action 'destroy' could not be found for UsersController test/controllers/users_controller_test.rb:49:in block (2 levels) in <class:UsersControllerTest>' test/controllers/users_controller_test.rb:48:inblock in '

34 runs, 133 assertions, 0 failures, 3 errors, 0 skips

2) When I immediately reissue the command without doing anything else, I get the following -- different -- result:

$ bundle exec rake test

Run options: --seed 13168

Running:

..................................

Finished in 1.065538s, 31.9088 runs/s, 129.5121 assertions/s.

34 runs, 138 assertions, 0 failures, 0 errors, 0 skips

3) I'm running this in a Cloud9 environment on a MacBook Pro

Thanks for the help.