Constant KTSTR_TEST_KERNEL_ENV 

pub const KTSTR_TEST_KERNEL_ENV: &str = "KTSTR_TEST_KERNEL";

Name of the environment variable that overrides the kernel path the eval dispatch reads (orthogonal to KTSTR_KERNEL_ENV which the main entry points use). Read at crate::test_support::eval::resolve_test_kernel: a set-but-empty KTSTR_TEST_KERNEL= surfaces a KTSTR_TEST_KERNEL not found: hard error (typo-loud per reader comment); ONLY the unset / Err(NotPresent) case falls through to crate::find_kernel() (cache + sysroot probes), which themselves fall through to a KernelUnavailable error hinting at both KTSTR_TEST_KERNEL and KTSTR_KERNEL.