Pre-testing is an alternative to pre-washing. Cut off a square inch of fabric, toss it into a clear glass of water, and wait to see if dye starts bleeding into the water. Afterwards, rub the wet fabric against a white fabric to see if any dye crocks (transfers). If a swatch passes both of these tests, it's safe to use.
I should add that pre-washing only gets rid of excess dye in a fabric. It will not permanently set dye that was not chemically set properly in the factory. Thus, you can pre-wash and still have a bleeding fabric on your hands. That's why it's a good idea to wash a bleeder fabric in Retayne before using it in a quilt (following up with a test swatch after the Retayne to make sure that it has stopped bleeding; some fabrics require two doses of Retayne).