Implement rev (#56)

* Implement `rev`

* Use uucore facility for error reporting

tests/by-util/test_rev.rs

@@ -0,0 +1,12 @@
+// This file is part of the uutils util-linux package.
+//
+// For the full copyright and license information, please view the LICENSE
+// file that was distributed with this source code.
+// spell-checker:ignore (words) symdir somefakedir
+
+use crate::common::util::TestScenario;
+
+#[test]
+fn test_invalid_arg() {
+    new_ucmd!().arg("--definitely-invalid").fails().code_is(1);
+}

tests/tests.rs

@@ -16,3 +16,7 @@ mod test_mountpoint;
 #[cfg(feature = "ctrlaltdel")]
 #[path = "by-util/test_ctrlaltdel.rs"]
 mod test_ctrlaltdel;
+
+#[cfg(feature = "rev")]
+#[path = "by-util/test_rev.rs"]
+mod test_rev;