So. You want faster rails tests so you can spend less time waiting for rake and more time sipping gatorpagne. I get it.

Step 1 - Garbage Collection Tuning (system change)

Add the following to your .bash_profile. It's based off the 37 signals REE tuning.

# Ruby GC Tuning
export RUBY_HEAP_MIN_SLOTS=600000
export RUBY_GC_MALLOC_LIMIT=59000000
export RUBY_HEAP_FREE_MIN=100000

This step by itself improves performance quite a bit.

Step 2 - Use a performance tweaked verison of ruby locally (system change)

Follow Funny Falcon's guides to performance improvements.

Step 3 - Allow garbage to be picked up (code change)

Follow Jamis' Guide to faster tests for, scrub_instance_variables. code.

Step 4 - MySQL Tuning (system change)

• On a Mac I used /usr/local/mysql/support-files/my-huge.cnf as a base and set innodb_buffer_pool_size=1G, which was about 10x what it was before.
• This change went from having tests take: 24 minutes, 39.146 seconds to 12 minutes, 41.172 seconds on our integration server.

Detailed Results with Analysis

• Step 1 - GC Tuning
• Step 2 - Patched Ruby
• Step 3 - Jamis' IVar Scrubbing
• Step 4 - MySQL Tuning

Net Results

Before: 37 minutes, 52.093 seconds
After:  12 minutes, 44.954 seconds
Savings: 25 minutes, 7.193 seconds, 

66.335% faster overall on our CI environment