Add sections about testing concurrency and stdout/err capture#37766

Merged

bors merged 3 commits intorust-lang:masterfrom

tarka:book-testing-concurrency-capture

Nov 17, 2016

Commits on Nov 14, 2016

Add sections about concurrency and stdout/err capture to the Testing chapter of the book.
Steve Smith
committed
Typo in new section
Steve Smith
committed
Remove thread-per-CPU bit as it may not be accurate.
Steve Smith
committed