error[E0658]: use of unstable library feature 'custom_test_frameworks': custom test frameworks are an unstable feature
  --> tests/ui/05-missing-features.rs:28:1
   |
28 | #[substance_test]
   | ^^^^^^^^^^^^^^^^^
   |
   = note: see issue #50297 <https://github.com/rust-lang/rust/issues/50297> for more information
   = help: add `#![feature(custom_test_frameworks)]` to the crate attributes to enable
   = note: this error originates in the attribute macro `substance_test` (in Nightly builds, run with -Z macro-backtrace for more info)