Add panic unit tests

src/libstd/f32.rs

@@ -1777,4 +1777,22 @@ mod tests {
         assert_ne!(nan_masked & QNAN_MASK, 0);
         assert!(nan_masked_fl.is_nan());
     }
+
+    #[test]
+    #[should_panic]
+    fn test_clamp_min_greater_than_max() {
+        1.0f32.clamp(3.0, 1.0);
+    }
+
+    #[test]
+    #[should_panic]
+    fn test_clamp_min_is_nan() {
+        1.0f32.clamp(NAN, 1.0);
+    }
+
+    #[test]
+    #[should_panic]
+    fn test_clamp_max_is_nan() {
+        1.0f32.clamp(3.0, NAN);
+    }
 }

src/libstd/f64.rs

@@ -1668,4 +1668,22 @@ mod tests {
         assert_approx_eq!(f64::from_bits(0x4094e40000000000), 1337.0);
         assert_approx_eq!(f64::from_bits(0xc02c800000000000), -14.25);
     }
+
+    #[test]
+    #[should_panic]
+    fn test_clamp_min_greater_than_max() {
+        1.0f64.clamp(3.0, 1.0);
+    }
+
+    #[test]
+    #[should_panic]
+    fn test_clamp_min_is_nan() {
+        1.0f64.clamp(NAN, 1.0);
+    }
+
+    #[test]
+    #[should_panic]
+    fn test_clamp_max_is_nan() {
+        1.0f64.clamp(3.0, NAN);
+    }
 }

src/libstd/lib.rs

@@ -249,6 +249,7 @@
 #![feature(cfg_target_vendor)]
 #![feature(char_error_internals)]
 #![feature(char_internals)]
+#![feature(clamp)]
 #![feature(collections_range)]
 #![feature(compiler_builtins_lib)]
 #![feature(const_fn)]