Introduce a test for `cp'.

Makefile

@@ -129,6 +129,7 @@ INSTALLEES  := \
 # Programs with usable tests
 TEST_PROGS  := \
   cat \
+  cp \
   mkdir \
   nl \
   seq \

test/cp.rs

@@ -0,0 +1,37 @@
+use std::io::process::Command;
+use std::io::File;
+use std::io::fs::{unlink, PathExtensions};
+
+static EXE: &'static str = "./cp";
+static TEST_HELLO_WORLD_SOURCE: &'static str = "hello_world.txt";
+static TEST_HELLO_WORLD_DEST: &'static str = "copy_of_hello_world.txt";
+
+fn cleanup(filename: &'static str) {
+    let path = Path::new(filename);
+    if path.exists() {
+        unlink(&path).unwrap();
+    }
+}
+
+
+#[test]
+fn test_cp_cp() {
+    // Invoke our binary to make the copy.
+    let prog = Command::new(EXE)
+                            .arg(TEST_HELLO_WORLD_SOURCE)
+                            .arg(TEST_HELLO_WORLD_DEST)
+                            .status();
+
+    // Check that the exit code represents a successful copy.
+    let exit_success = prog.unwrap().success();
+    assert_eq!(exit_success, true);
+
+    // Check the content of the destination file that was copied.
+    let contents = File::open(&Path::new(TEST_HELLO_WORLD_DEST))
+                            .read_to_string()
+                            .unwrap();
+    assert_eq!(contents.as_slice(), "Hello, World!\n");
+
+    cleanup(TEST_HELLO_WORLD_SOURCE);
+    cleanup(TEST_HELLO_WORLD_DEST);
+}

test/fixtures/cp/hello_world.txt

@@ -0,0 +1 @@
+Hello, World!