`rake` and `rake test` fails

Running `rake` or `rake test` fails with the following (with and without `bundle exec`):

``` sh
➜ github-ldap git:(feature/multi_domain) rake
/Users/davesims/github/github-ldap/test/test_helper.rb:20:in `': undefined method `after_run' for MiniTest:Module (NoMethodError)
from /Users/davesims/github/github-ldap/test/domain_test.rb:1:in `require_relative'
from /Users/davesims/github/github-ldap/test/domain_test.rb:1:in `'
from /Users/davesims/github/github/vendor/ruby/11323111113067d8fc579071c01d83e9f161adc4/lib/ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require'
from /Users/davesims/github/github/vendor/ruby/11323111113067d8fc579071c01d83e9f161adc4/lib/ruby/2.1.0/rubygems/core_ext/kernel_require.rb:55:in `require'
from /Users/davesims/github/github/vendor/gems/2.1.7/bundler/../ruby/2.1.0/gems/rake-10.5.0/lib/rake/rake_test_loader.rb:10:in `block (2 levels) in '
from /Users/davesims/github/github/vendor/gems/2.1.7/bundler/../ruby/2.1.0/gems/rake-10.5.0/lib/rake/rake_test_loader.rb:9:in `each'
from /Users/davesims/github/github/vendor/gems/2.1.7/bundler/../ruby/2.1.0/gems/rake-10.5.0/lib/rake/rake_test_loader.rb:9:in `block in '
from /Users/davesims/github/github/vendor/gems/2.1.7/bundler/../ruby/2.1.0/gems/rake-10.5.0/lib/rake/rake_test_loader.rb:4:in `select'
from /Users/davesims/github/github/vendor/gems/2.1.7/bundler/../ruby/2.1.0/gems/rake-10.5.0/lib/rake/rake_test_loader.rb:4:in `'
rake aborted!
Command failed with status (1): [ruby -I"lib:test" -I"/Users/davesims/github/github/vendor/gems/2.1.7/bundler/../ruby/2.1.0/gems/rake-10.5.0/lib" "/Users/davesims/github/github/vendor/gems/2.1.7/bundler/../ruby/2.1.0/gems/rake-10.5.0/lib/rake/rake_test_loader.rb" "test/**/*_test.rb" ]

Tasks: TOP => default => test
(See full trace by running task with --trace)
```

Workaround is to run test files directly through ruby & bundler

``` sh
➜ github-ldap git:(feature/multi_domain) bundle exec ruby -Ilib:test test/**/*_test.rb
Run options: --seed 6062

# Running:

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

Finished in 3.112345s, 16.7077 runs/s, 23.4550 assertions/s.

52 runs, 73 assertions, 0 failures, 0 errors, 0 skips
```

MiniTest.after_run が報告されたエラーを発生させる test/test_helper.rb:20 から始め、次に rake と rake test を実行して再現します。これらの結果を、issue に示されている ruby の直接的なテストコマンドと比較します。両方の Rake コマンドが正常に完了し、テストスイートがパスすれば完了です。

索引モデルが issue の本文から書いたものです。