Apple - How to stress a MacBook Pro Retina?

Consuming All the CPU Cores

The command below runs a yes instance for each CPU core and consumes a near maximum of the computer's processing capability:

CPU=$(sysctl -n hw.ncpu)
seq $CPU | xargs -I{} -P $CPU yes > /dev/null

The command builds upon Mike's answer, but runs multiple instances of yes with xargs. One yes process will max out a CPU core, so multiple processes are needed. Thanks to @lights0123 for refining this command.

This deals with the CPU but not GPU or RAM.

CPU + GPU = WebGL

To stress the CPU and GPU, visit ShibuyaCrowd, a WebGL experiment (open source).

A minute after running this site, your MacBook Pro should be under reasonable computational load.

Just enter the command yes > /dev/null in a Terminal session. That will max out a CPU core until you Ctrl-C it or close the Terminal window.