I have heard there is something called a jumper that I'm going to have to use to leak test my water cooling loop when I finish it that powers the loop without powering the rest of the components.
A power supply jumper allows you to turn on the power supply without having to connect it to any component except the pump. This is because 2 of the pins in the 24pin connector control PSU startup, so by connecting them with a jumper (or just a paperclip really, just have to get the pins right) the PSU turns on. Then, once you're done, you just turn off the PSU from the switch it has on its back. While doing this
everything except the pump has to be disconnected from the power supply. The motherboard connectors
and the connectors going to graphics cards or SATA drives
have to be disconnected. You can use this to test the fans as well by using a 3pin fan to molex adapter to connect the fans directly to the power supply (this runs them at their max speed so don't be alarmed by the noise if you do this).
Why? Just have to connect positive to positive and negative to negative, although you would need a couple wires to do the battery method.