Needs environment variable

Skip code (such as a test) at compile time if an environment variable is undefined.

Example

some_test will not be compiled if SOMEENVIRONMENTVARIABLE is not defined:

#[needs_env_var(SOMEENVIRONMENTVARIABLE)]
#[test]
fn some_test() {
    assert!(1 == 1);
}

Note: As needs_env_var is evaluated at compile time you need to force a re-compilation an environment variable is defined after compilation, e.g. with cargo clean.