RSpec is not the reason your rails test suite is slow

output.txt

[david: compare]$ # at this point we have a stock rails app with no minitest tests and one pending rspec example
[david: compare]$ 
[david: compare]$ time rake test
Run options: 

# Running tests:



Finished tests in 0.030419s, 0.0000 tests/s, 0.0000 assertions/s.

0 tests, 0 assertions, 0 failures, 0 errors, 0 skips

real	0m5.694s
user	0m4.503s
sys	0m0.811s
[david: compare]$ time rake spec
/Users/david/.rvm/rubies/ruby-1.9.3-p0/bin/ruby -S rspec ./spec/models/thing_spec.rb
*

Pending:
  Thing add some examples to (or delete) /Users/david/tmp/compare/spec/models/thing_spec.rb
    # No reason given
    # ./spec/models/thing_spec.rb:4

Finished in 0.00072 seconds
1 example, 0 failures, 1 pending

real	0m4.918s
user	0m3.839s
sys	0m0.697s
[david: compare]$ 
[david: compare]$ echo 'require "test_helper"
> 
> class ThingTest < ActiveSupport::TestCase
>   test "empty" do
>   end
> end
> ' > test/unit/thing_test.rb
[david: compare]$ 
[david: compare]$ echo 'require "spec_helper"
> 
> describe Thing do
>   example "empty" do
>   end
> end
> ' > spec/models/thing_spec.rb
[david: compare]$ 
[david: compare]$ time rake test
Run options: 

# Running tests:

.

Finished tests in 0.078296s, 12.7720 tests/s, 0.0000 assertions/s.

1 tests, 0 assertions, 0 failures, 0 errors, 0 skips

real	0m5.802s
user	0m4.565s
sys	0m0.847s
[david: compare]$ time rake spec
/Users/david/.rvm/rubies/ruby-1.9.3-p0/bin/ruby -S rspec ./spec/models/thing_spec.rb
.

Finished in 0.00475 seconds
1 example, 0 failures

real	0m4.950s
user	0m3.903s
sys	0m0.725s
[david: compare]$ 
[david: compare]$ echo 'require "test_helper"
> 
> class ThingTest < ActiveSupport::TestCase
>   1000.times.map do |n|
>     test "empty #{n}" do
>     end
>   end
> end
> ' > test/unit/thing_test.rb
[david: compare]$ 
[david: compare]$ echo 'require "spec_helper"
> 
> describe Thing do
>   1000.times.map do |n|
>     example "empty #{n}" do
>     end
>   end
> end
> ' > spec/models/thing_spec.rb
[david: compare]$ 
[david: compare]$ time rake test
Run options: 

# Running tests:

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

Finished tests in 0.753860s, 1326.5062 tests/s, 0.0000 assertions/s.

1000 tests, 0 assertions, 0 failures, 0 errors, 0 skips

real	0m6.730s
user	0m5.047s
sys	0m0.887s
[david: compare]$ time rake spec
/Users/david/.rvm/rubies/ruby-1.9.3-p0/bin/ruby -S rspec ./spec/models/thing_spec.rb
........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................

Finished in 0.99978 seconds
1000 examples, 0 failures

real	0m6.023s
user	0m4.615s
sys	0m0.790s

script.sh

rails new compare
cd compare
rails g model thing name:string
echo "gem 'rspec-rails', '2.9.0.rc2', :group => [:development, :test]" >> Gemfile
bundle
rails g rspec:install
rails g model thing name:string --skip-migration
rake db:migrate
rake db:test:prepare

# at this point we have a stock rails app with no minitest tests and one pending rspec example

time rake test
time rake spec

echo 'require "test_helper"

class ThingTest < ActiveSupport::TestCase
  test "empty" do
  end
end
' > test/unit/thing_test.rb

echo 'require "spec_helper"

describe Thing do
  example "empty" do
  end
end
' > spec/models/thing_spec.rb

time rake test
time rake spec

echo 'require "test_helper"

class ThingTest < ActiveSupport::TestCase
  1000.times.map do |n|
    test "empty #{n}" do
    end
  end
end
' > test/unit/thing_test.rb

echo 'require "spec_helper"

describe Thing do
  1000.times.map do |n|
    example "empty #{n}" do
    end
  end
end
' > spec/models/thing_spec.rb

time rake test
time rake spec

Gary Bernhardt does a great job of showing how to reduce test dependencies at https://www.destroyallsoftware.com

+1 to both DAS and Objects On Rails. Those were my sources of techniques to speed up my test suite.