If your tests are failing with an out of memory message like:
Error: ENOMEM: not enough memory, read
Check to see if you have broccoli-babel-transpiler in your dependency tree. It added a feature recently to autodetect multiple cores and run at higher parallelism. Someone recently posted in this Ember.js issue thread about setting JOBS=1 in the environment to fix this. If you use this plugin directly or indirectly, you may need to do the same.