How do you test an op-amp for oscillation and what are the symptoms of an op-amp that is oscillating? Also, if it is a two channel op-amp can you get oscillation on just one channel?

Here are some pictures of the two Clones that I built. I tried to keep them as close to authentic as I could. I made my own circuit boards and poplulated them with Solen Caps, NJM-4556 op-amp, Vishay resistors, RS-Alps Pot 100k, I also used Neutrik 1/4" jacks. The boxes are old cigar boxes a...