split_tests

#!/bin/bash

# Split test files between multiple boxes.
#
# Finds files within the paths/options given, and picks a consistent slice of them based
# on "what box this is out of how many".
#
# Requires:
#   - parameters with the paths/options to send to `find`
#   - environment variables BOX_COUNT (1-based) and BOX_INDEX (0-based) specifying how
#     many boxes we are splitting between, and which one is "this one"
#
# Example rspec usage: `rspec $(./split_tests spec/some_dir -name "*_spec.rb")`
#
# If you want to test this script locally and manually set the env variables in the command itself:
# `echo $(BOX_INDEX=0 BOX_COUNT=3 ./split_tests spec/some_dir -name "*_spec.rb")`
#
# How it works:
# The `NR` variable in awk tells us which row of the input we're processing, so taking the
# modulo against the BOX_COUNT tells us which box to run it in. Comparing it to the current
# BOX_INDEX lets us decide whether to return that file to pass over to the test runner,
# or skip it.

find $@ | sort | awk "NR % $BOX_COUNT == $BOX_INDEX"