Improve core::cmp coverage

Author: pvdrz

library/coretests/tests/cmp.rs

@@ -118,6 +118,13 @@ fn test_user_defined_eq() {
     assert!(SketchyNum { num: 25 } != SketchyNum { num: 57 });
 }
 
+#[test]
+fn test_clamp() {
+    assert_eq!((-3).clamp(-2, 1), -2);
+    assert_eq!(0.clamp(-2, 1), 0);
+    assert_eq!(2.clamp(-2, 1), 1);
+}
+
 #[test]
 fn ordering_const() {
     // test that the methods of `Ordering` are usable in a const context