> When running tests I am a fan of being able to split my screen so I can view the tests alongside code. Tmux worked well for this, however it comes with a few disadvantages. Pasting code between Tmux and Vim panes required use of the system register which is a pain.
I'm personally not a fan of them, but why wouldn't you use vim split panes?
Maybe he meant he was running the tests in the split, and copy/pasting bits of text between the editor and shell.
He could also have used tmux's copy buffer, but it is a little cumbersome.