Add initial tests for realpath.

Makefile

@@ -178,6 +178,7 @@ TEST_PROGS  := \
   ptx \
   pwd \
   readlink \
+  realpath \
   rm \
   seq \
   sort \

test/realpath.rs

@@ -0,0 +1,46 @@
+use std::process::Command;
+use std::str;
+use util::*;
+
+static PROGNAME: &'static str = "./realpath";
+
+#[path = "common/util.rs"]
+#[macro_use]
+mod util;
+
+#[test]
+fn test_current_directory() {
+    let po = Command::new(PROGNAME)
+        .arg(".")
+        .output()
+        .unwrap_or_else(|err| panic!("{}", err));
+
+    let out = str::from_utf8(&po.stdout[..]).unwrap().trim_right();
+    assert_eq!(out, current_directory());
+}
+
+#[test]
+fn test_long_redirection_to_current_dir() {
+    // Create a 256-character path to current directory
+    let dir = repeat_str("./", 128);
+    let po = Command::new(PROGNAME)
+        .arg(dir)
+        .output()
+        .unwrap_or_else(|err| panic!("{}", err));
+
+    let out = str::from_utf8(&po.stdout[..]).unwrap().trim_right();
+    assert_eq!(out, current_directory());
+}
+
+#[test]
+fn test_long_redirection_to_root() {
+    // Create a 255-character path to root
+    let dir = repeat_str("../", 85);
+    let po = Command::new(PROGNAME)
+        .arg(dir)
+        .output()
+        .unwrap_or_else(|err| panic!("{}", err));
+
+    let out = str::from_utf8(&po.stdout[..]).unwrap().trim_right();
+    assert_eq!(out, "/");
+}