There are a few ways you can test car speakers to ensure they are working properly:

1. Play a variety of music that includes a range of frequencies, such as bass, mid-range, and treble, to see how well the speakers handle each frequency. You can also use a frequency sweep test tone to specifically test how well the speakers handle certain frequencies.
2. Play music at different volume levels to see how well the speakers handle both low and high volumes.
3. Use a multimeter to test the electrical resistance of the speakers. This can help you determine if there are any problems with the speaker's wiring or connections.
4. Listen for any distortion or issues with sound quality. If you notice any problems, it could be an indication that the speakers are damaged or not functioning properly.

Overall, it's important to test car speakers using a variety of methods to get a comprehensive understanding of their performance.