prism creating ‘a.out’ files?

I’ve got sendgrid-php as part of my custom theme, and I saw there’s a Go program called ‘prism’ that’s part of it. I thought nothing of it, until today when a new ‘a.out’ appeared in the same directory.

The CHANGELOG.md says “Tests now mocked automatically against prism”, but I don’t understand what it’s for. and seeing a new compiled program written in Go named ‘a.out’ appear next to it makes me very very nervous.

What does ‘prism’ do? And should it be compiling new programs alongside it? My instincts tell me I’ve been hacked.