Ever wanted to modify an ENV variable, an instance or class variable (e.g. on Config) for the duration of a block or for all tests of a “describe” group? This pattern emerged repeatedly in my suites and as I don’t like to bloat my test/spec helper, about time for the lightweight and dependency-free minitest-substitute gem. Drop cumbersome before and after handling with one or more easy to read with "ENV['FOO']", "bar" or with "@run_at", on: Config { Time.now } declarations. Happy testing!