Voices aren't inherently good or bad, they just are.

To test how well you can sing, just record yourself singing something you like and then play it back to see if you hit the notes you were trying to hit.

Some components of good singing are: matching pitch, holding pitch, controlling dynamics, controlling vibrato, and good production with focused breath. A lot of these depend on having a good ear and sensitivity to the musical context, not just the quality of the voice itself. The first step of any good art is to observe well (listening for musicians, seeing for visual artists, feeling for all artists).

If you listen to yourself and find yourself wobbly on pitch, overly breathy, or not matching well with the musical context and artistic intent, you still have work to do. Hint: We all always still have work to do. :)