tests(readme): Use skeptic to test the readme

serde_macros/tests/skeptic.rs

@@ -0,0 +1,3 @@
+#![cfg(feature = "nightly-testing")]
+
+include!(concat!(env!("OUT_DIR"), "/skeptic-tests.rs"));

serde_macros/tests/test.rs

@@ -6,3 +6,4 @@ extern crate test;
 include!("../../testing/tests/test.rs.in");
 
 mod compile_tests;
+mod skeptic;