Rollup merge of #147195 - hkBst:repeat-3, r=Mark-Simulacrum

iter repeat: add tests for new count and last behavior

Tests for https://github.com/rust-lang/rust/pull/146410

library/coretests/tests/iter/sources.rs

@@ -30,6 +30,17 @@ fn test_repeat_take_collect() {
     assert_eq!(v, vec![42, 42, 42]);
 }
 
+#[test]
+#[should_panic = "iterator is infinite"]
+fn test_repeat_count() {
+    repeat(42).count();
+}
+
+#[test]
+fn test_repeat_last() {
+    assert_eq!(repeat(42).last(), Some(42));
+}
+
 #[test]
 fn test_repeat_with() {
     #[derive(PartialEq, Debug)]