A slightly more expensive option is to use an electronic load (like this). You can find them online for as low as 20 bucks (got mine for free after getting a refund from a supplier in China since it took nearly 6 months to arrive and we thought it had been lost by the courier).
EDIT: I am not saying that you need to wait 6 months for it to arrive. By the time I finally got my first electronic load, I had already purchased another one from a local supplier for nearly £35. It was worth paying the extra money as I needed it with a bit of urgency ;)
With an electronic load, you can accurately vary the current demand and get readings of power being delivered and even set timers for the stability of your circuit.
Here are two examples of what you can get at different price ranges: