No, unfortunately, there is no way of testing a GPU without using a PC. This is because the GPU needs to have a source of power in order for it to run, as well as a PCIe lane to receive and send instructions.
If you want to find out benchmarking or stress test results of a GPU and cannot run it on a PC, it is always best to check the manufacturers' website to see if they have any testing results. In addition to this, there are many websites that are dedicated to testing this.