"A good mentality to get into is try not to leave the editor. Don't make committing the code a leave-the-editor activity. Don't make running tests a leave the editor activity. Stay in Vim." (#)
"It's all about speed!: you don't have to leave your editor to do it - just edit and save. This works especially great when you have a tool that reruns your tests on file-save (like testem)." (#)
34:30 "Justin: If it's faster to use a REPL to answer the question of 'If I do X will I get Y?', people will use the REPL and then as soon as the REPL session is over, it goes away forever. But if it's equally fast to just codify that in a quick test or check like it is in Smalltalk or, even environments like Java where your IDE you just hit ctrl-r and it will run the tests under the line in a half second. It definitely reduces that cost." (#)