spec.rb

# Note the differences between this and https://gist.github.com/2938965 are that
# we're making 10k groups with 2 examples each vs 10k group w/ 1 example.

if $0 =~ /rspec$/
  10_000.times do |i|
    describe "loltest #{i}" do
      it "does #{i}" do
        i.should eq i
      end

      it "does #{i}" do
        i.should eq i
      end
    end
  end
else
  require 'minitest/autorun'

  10_000.times do |i|
    describe "loltest #{i}" do
      it "does #{i}" do
        i.must_equal i
      end

      it "does #{i}" do
        i.must_equal i
      end
    end
  end
end

__END__
On my machine:

$ time ruby spec.rb 
Run options: --seed 25270

# Running tests:

[dots omitted]

Finished tests in 6.723914s, 2974.4580 tests/s, 2974.4580 assertions/s.

20000 tests, 20000 assertions, 0 failures, 0 errors, 0 skips

real	0m12.153s
user	0m10.144s
sys	0m0.329s

$ time rspec spec.rb 

[dots omitted]

Finished in 7.4 seconds
20000 examples, 0 failures

real	0m16.510s
user	0m9.704s
sys	0m0.968s