Really love these videos, they cover a broad range of practical stuff which just doesn't get covered elsewhere. Everyone should be integration testing their handlers, but I suspect most don't, even though the go http packages make it pretty easy.
Go is not an object-oriented language. ...It’s better to compose than inherit
This depends of course on your definition of Object Oriented, but I think it captures an important truth - Go is in many ways a rejection of modern OO programming, with all the ceremony and hierarchy that it involves, so though this idea is contentious, Go has dumped all of that in favour of composition. Nowadays when people talk about OOP, they really mean objects and inheritance.
Channels and goroutines are powerful way to solve problems involving concurrency
While I think channels are nice, they're also often overused by newcomers to the language.
There is nothing exceptional in exceptions
I do love this about go. Just wish they had completely left out panic, and perhaps had some sugar to make it slightly less painful to return an error (go is becoming infamouse for if err != nil which is a shame).
This does seem a little biased because the author is not writing server software, which is really the intended use of context. It does feel like cancellation is something that would be better built into goroutines though, rather than tacked on to every api.
Context may still be required in web apps though in order to thread request specific data through various levels of handlers/middleware.