test(headers): Add tests for single value headers.

src/header/common/referer.rs

@@ -14,6 +14,11 @@ header! {
     #[doc="```"]
     // TODO: Use URL
     (Referer, "Referer") => [String]
+
+    test_referer {
+        // Testcase from the RFC
+        test_header!(test1, vec![b"http://www.example.org/hypertext/Overview.html"]);
+    }
 }
 
 bench_header!(bench, Referer, { vec![b"http://foo.com/hello:3000".to_vec()] });