tr: implement complement separately from delete or squeeze (#2147)

tests/by-util/test_tr.rs

@@ -45,6 +45,33 @@ fn test_delete_complement() {
         .stdout_is("ac");
 }
 
+#[test]
+fn test_complement1() {
+    new_ucmd!()
+        .args(&["-c", "a", "X"])
+        .pipe_in("ab")
+        .run()
+        .stdout_is("aX");
+}
+
+#[test]
+fn test_complement2() {
+    new_ucmd!()
+        .args(&["-c", "0-9", "x"])
+        .pipe_in("Phone: 01234 567890")
+        .run()
+        .stdout_is("xxxxxxx01234x567890");
+}
+
+#[test]
+fn test_complement3() {
+    new_ucmd!()
+        .args(&["-c", "abcdefgh", "123"])
+        .pipe_in("the cat and the bat")
+        .run()
+        .stdout_is("3he3ca33a3d33he3ba3");
+}
+
 #[test]
 fn test_squeeze() {
     new_ucmd!()