How to tell if potting soil is bad?

Can you explain how one can identify if potting soil has gone bad? Are there any specific signs or indicators that I should be looking out for? Perhaps there are certain changes in the soil's texture, color, or smell that might suggest it's no longer suitable for plant growth. I'm keen to learn more about the process of assessing the quality of potting soil and what steps to take if it's deemed unsuitable for use.