Add test infrastructure to work directly with frames (#56)

This adds a `Codec` based testing API. This is a bit less annoying than writing
at the raw H2 wire protocol level...

tests/support/src/assert.rs

@@ -0,0 +1,50 @@
+
+#[macro_export]
+macro_rules! assert_closed {
+    ($transport:expr) => {{
+        assert_eq!($transport.poll().unwrap(), None.into());
+    }}
+}
+
+#[macro_export]
+macro_rules! assert_ping {
+    ($frame:expr) => {{
+        match $frame {
+            ::h2::frame::Frame::Ping(v) => v,
+            f => panic!("expected PING; actual={:?}", f),
+        }
+    }}
+}
+
+#[macro_export]
+macro_rules! assert_settings {
+    ($frame:expr) => {{
+        match $frame {
+            ::h2::frame::Frame::Settings(v) => v,
+            f => panic!("expected SETTINGS; actual={:?}", f),
+        }
+    }}
+}
+
+#[macro_export]
+macro_rules! poll_err {
+    ($transport:expr) => {{
+        match $transport.poll() {
+            Err(e) => e,
+            frame => panic!("expected error; actual={:?}", frame),
+        }
+    }}
+}
+
+#[macro_export]
+macro_rules! poll_data {
+    ($transport:expr) => {{
+        use h2::frame::Frame;
+        use futures::Async;
+
+        match $transport.poll() {
+            Ok(Async::Ready(Some(Frame::Data(frame)))) => frame,
+            frame => panic!("expected data frame; actual={:?}", frame),
+        }
+    }}
+}