I'd like to have some feedback on the pi hardware, without having to use a screen or monitor.
Is it possible to trigger through code? I know that resin.io can flash the light from their software.
I'm running on raspbian atm.
I'm going to guess you mean one of the LEDs.
The (green) activity LED can be written.
On early model Pis it is connected to gpio16 and is active low (i.e. writing 0 switches it on, 1 switches it off).
On the A+/B+/Pi2/compute modules it is connected to gpio47 and is active high.
It is also possible to control the other LEDs but that is a bit more advanced and requires a software download. Google may find that software.