I believe this should work, and I just verify that it works on Windows 10.
And I notice that the environment is created at "/tmp/testenv"
but in the JuliaCall script, the path is "/tmp/testproj". Is this a typo, or is it the actual code?
One quick thing to check is that JuliaCall has some julia package dependencies like RCall, which should be installed into the environment at "/tmp/testproj" if JuliaCall “correctly” picks that environment, otherwise JuliaCall won’t be able to finish loading the setup script.