robot-name: remove redundant tests

part of #1824

This is another case where I think it makes sense to actually keep the util
function around. It produces a good error message and in combination with the
body of the test function, users should have enough information.

exercises/practice/robot-name/tests/robot-name.rs

@@ -12,27 +12,12 @@ fn assert_name_matches_pattern(n: &str) {
     );
 }
 
-fn assert_name_is_persistent(r: &robot::Robot) {
-    // The type system already proves this, but why not.
-    let n1 = r.name();
-    let n2 = r.name();
-    let n3 = r.name();
-    assert_eq!(n1, n2);
-    assert_eq!(n2, n3);
-}
-
 #[test]
 fn name_should_match_expected_pattern() {
     let r = robot::Robot::new();
     assert_name_matches_pattern(r.name());
 }
 
-#[test]
-#[ignore]
-fn name_is_persistent() {
-    assert_name_is_persistent(&robot::Robot::new());
-}
-
 #[test]
 #[ignore]
 fn different_robots_have_different_names() {
@@ -63,14 +48,6 @@ fn new_name_should_match_expected_pattern() {
     assert_name_matches_pattern(r.name());
 }
 
-#[test]
-#[ignore]
-fn new_name_is_persistent() {
-    let mut r = robot::Robot::new();
-    r.reset_name();
-    assert_name_is_persistent(&r);
-}
-
 #[test]
 #[ignore]
 fn new_name_is_different_from_old_name() {