RuntimeException : Unable to guess the Kernel directory
I think I had the exact same issue few weeks ago, can you try adding KERNEL_DIR:
<php> <ini name="error_reporting" value="-1" /> <server name="KERNEL_CLASS" value="AppKernel" /> <server name="KERNEL_DIR" value="app/" /> <env name="SYMFONY_DEPRECATIONS_HELPER" value="weak"/></php>
./vendor/bin/simple-phpunit -c app/ add the Appkernel directory which is app while executing the command for testing.