Justin Searls on Twitter
Matt Swanson on Twitter

Arrows
Test Double

Justin's "What do you like about RSpec" thread (2016)
Dan North BDD
Nate Berkopec "Reading rspec documentation like..." tweet
Corey Haines: Fast Rails Tests
Kent Beck: "I get paid for code that works, not for tests..."
Nick Quaranto's minitest CLI wrapper
Mocktail gem
test_data gem