use assert_cmd::prelude::*; // Add methods on commands use predicates::prelude::*; // Used for writing assertions use std::process::Command; // Run programs #[test] fn file_doesnt_exist() -> Result<(), Box> { let mut cmd = Command::cargo_bin("grrs")?; cmd.arg("foobar").arg("test/file/doesnt/exist"); cmd.assert() .failure() .stderr(predicate::str::contains("could not read file")); Ok(()) }