coretest: Ensure that pointer formatting flags are cleaned up

src/libcoretest/fmt/mod.rs

@@ -9,3 +9,10 @@
 // except according to those terms.
 
 mod num;
+
+#[test]
+fn test_format_flags() {
+    // No residual flags left by pointer formatting
+    let p = "".as_ptr();
+    assert_eq!(format!("{:p} {:x}", p, 16u), format!("{:p} 10", p));
+}