Add tests for readlink.

Makefile

@@ -172,6 +172,7 @@ TEST_PROGS  := \
   nl \
   paste \
   pwd \
+  readlink \
   seq \
   sort \
   split \

test/readlink.rs

@@ -0,0 +1,88 @@
+use std::env;
+use std::process::Command;
+use std::str;
+
+static PROGNAME: &'static str = "./readlink";
+static GIBBERISH: &'static str = "supercalifragilisticexpialidocious";
+
+fn current_directory() -> String {
+    env::current_dir().unwrap().into_os_string().into_string().unwrap()
+}
+
+fn repeat_str(s: &str, n: u32) -> String {
+    let mut repeated = String::new();
+    for _ in 0 .. n {
+        repeated.push_str(s);
+    }
+    repeated
+}
+
+#[test]
+fn test_canonicalize() {
+    let po = Command::new(PROGNAME)
+        .arg("-f")
+        .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_canonicalize_existing() {
+    let po = Command::new(PROGNAME)
+        .arg("-e")
+        .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_canonicalize_missing() {
+    let mut expected = current_directory();
+    expected.push_str("/");
+    expected.push_str(GIBBERISH);
+
+    let po = Command::new(PROGNAME)
+        .arg("-m")
+        .arg(GIBBERISH)
+        .output()
+        .unwrap_or_else(|err| panic!("{}", err));
+
+    let out = str::from_utf8(&po.stdout[..]).unwrap().trim_right();
+    assert_eq!(out, expected);
+}
+
+#[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("-n")
+        .arg("-m")
+        .arg(dir)
+        .output()
+        .unwrap_or_else(|err| panic!("{}", err));
+
+    let out = str::from_utf8(&po.stdout[..]).unwrap();
+    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("-n")
+        .arg("-m")
+        .arg(dir)
+        .output()
+        .unwrap_or_else(|err| panic!("{}", err));
+
+    let out = str::from_utf8(&po.stdout[..]).unwrap();
+    assert_eq!(out, "/");
+}