Setup bootsnap to speedup TestRunnerTest

[casperisfine]

When running rails t we skip the "fork" optimization. Because of this Rails is loaded from scratch.

However the vast majority of the code is Rails and other gems so it's the same for all tests.

By setting up bootsnap we can dramatically speed it up.

main:

$ bin/test test/application/test_runner_test.rb -n test_run_single_file
Run options: -n test_run_single_file --seed 8478

.

Finished in 7.313216s, 0.1367 runs/s, 0.2735 assertions/s.

This branch:

$ bin/test test/application/test_runner_test.rb -n test_run_single_file
Run options: -n test_run_single_file --seed 60063

.

Finished in 2.751576s, 0.3634 runs/s, 0.7269 assertions/s.
1 runs, 2 assertions, 0 failures, 0 errors, 0 skips

[casperisfine]

test/application/test_runner_test.rb
/usr/local/bin/ruby -w -Itest -Ilib -I../activesupport/lib -I../actionpack/lib -I../actionview/lib -I../activemodel/lib test/application/test_runner_test.rb
Run options: --seed 12870
 
# Running:
 
.....................................................................
 
Finished in 179.129634s, 0.3852 runs/s, 1.5352 assertions/s.
69 runs, 275 assertions, 0 failures, 0 errors, 0 skips

vs main

test/application/test_runner_test.rb
/usr/local/bin/ruby -w -Itest -Ilib -I../activesupport/lib -I../actionpack/lib -I../actionview/lib -I../activemodel/lib test/application/test_runner_test.rb
Run options: --seed 50206
 
# Running:
 
.....................................................................
 
Finished in 307.722595s, 0.2242 runs/s, 0.8937 assertions/s.
69 runs, 275 assertions, 0 failures, 0 errors, 0 skips

This job is no longer the CI bottleneck.

[p8]

Nice!