Add integration tests.

tests/hay.rs

@@ -0,0 +1,24 @@
+pub const SHERLOCK: &'static str = "\
+For the Doctor Watsons of this world, as opposed to the Sherlock
+Holmeses, success in the province of detective work must always
+be, to a very large extent, the result of luck. Sherlock Holmes
+can extract a clew from a wisp of straw or a flake of cigar ash;
+but Doctor Watson has to have it taken out for him and dusted,
+and exhibited clearly, with a label attached.
+";
+
+pub const CODE: &'static str = "\
+extern crate snap;
+
+use std::io;
+
+fn main() {
+    let stdin = io::stdin();
+    let stdout = io::stdout();
+
+    // Wrap the stdin reader in a Snappy reader.
+    let mut rdr = snap::Reader::new(stdin.lock());
+    let mut wtr = stdout.lock();
+    io::copy(&mut rdr, &mut wtr).expect(\"I/O operation failed\");
+}
+";