This shouldn't actually happen though, because of the Lmod guards the only scenario I can see where you would reach this is where you are using a container and the system drivers are too old

I triggered it by cleaning out the host_injections directory after loading the module.

I agree it's very unlikely that it happens, but we should mention it in the docs regardless, if only to let people easily find this page when searching for error messages.

My concern here is that the placement here makes it seem like it not working is likely, but reaching this message is actually very unlikely

Maybe a little box saying What does it look like if the command fails?

Currently, this only treats testing if you can run CUDA-enabled software from EESSI. Maybe we can also include a small instruction for testing if building new CUDA software on top of EESSI works properly. Something like this:
First, create a file hello_cuda.cu with the contents

#include <stdio.h>

__global__ void helloCUDA()
{
    printf("Hello, CUDA!\n");
}

int main()
{
    helloCUDA<<<1, 1>>>();
    cudaDeviceSynchronize();
    return 0;
}

Then

module load CUDA/<some_version>
nvcc -o hello_cuda.cu -o hello_cuda
chmod u+x hello_cuda
./hello_cuda 

And mention they should test this for each version of CUDA they installed in host_injections

Makes sense, but that should be done in a separate PR?

If you want, sure. I won't block this one over it :) Although I would consider it to be an integral part of "Testing the GPU support" to be honest :)

I don't see it as so integral if we are focused on software consumers, it's only integral if you want to do development-type work