Having helped on a local hobby-class where students build their own amps, I think you should consider also trying with speakers. We saw some amps becoming unstable because speakers can present a very, very messy load w.r.t. frequency (EG, some amps were fine into an 8 ohm dummy resistor, but were all over the place when we hooked up an 8-ohm rated speaker).
What I have seen people do to 'break in' speakers, is to take two of the same type, wire them 180 degrees out of phase (IE, hook one up 'backwards). Then point them at each other and move them close together.
They should cancel out most of the sound of each other, and while not perfectly silent, they will be much quieter than they would be when not facing each other (can always put them under a pile of pillows to really shut them up).
For initial testing, I have 2 big 10 ohm resistors.
First step: Do a no-load test, and just measure the DC/AC voltages with a multimeter (and/or scope if you know what you are doing).
Second test, if the first doesn't show crazy stuff: Hook up the dummy resistors and short the input of the amplifier. Again, measure with meters and bring up slowly.
Once I am confident they are not doing something crazy (like putting VCC or VSS on one of the outputs) I can hook up speakers to test fully.