Add tests for link.

Makefile

@@ -177,6 +177,7 @@ TEST_PROGS  := \
   fold \
   hashsum \
   head \
+  link \
   ln \
   mkdir \
   mv \

test/common/util.rs

@@ -64,6 +64,11 @@ pub fn get_file_contents(name: &str) -> String {
     contents
 }
 
+pub fn set_file_contents(name: &str, contents: &str) {
+    let mut f = File::open(Path::new(name)).unwrap();
+    let _ = f.write(contents.as_bytes());
+}
+
 pub fn mkdir(dir: &str) {
     fs::create_dir(Path::new(dir)).unwrap();
 }

test/link.rs

@@ -0,0 +1,49 @@
+extern crate libc;
+
+use std::process::Command;
+use util::*;
+
+static PROGNAME: &'static str = "./link";
+
+#[path = "common/util.rs"]
+#[macro_use]
+mod util;
+
+#[test]
+fn test_link_existing_file() {
+    let file = "test_link_existing_file";
+    let link = "test_link_existing_file_link";
+
+    touch(file);
+    set_file_contents(file, "foobar");
+    assert!(file_exists(file));
+
+    let result = run(Command::new(PROGNAME).args(&[file, link]));
+    assert_empty_stderr!(result);
+    assert!(result.success);
+    assert!(file_exists(file));
+    assert!(file_exists(link));
+    assert_eq!(get_file_contents(file), get_file_contents(link));
+}
+
+#[test]
+fn test_link_no_circular() {
+    let link = "test_link_no_circular";
+
+    let result = run(Command::new(PROGNAME).args(&[link, link]));
+    assert_eq!(result.stderr, "link: error: No such file or directory (os error 2)\n");
+    assert!(!result.success);
+    assert!(!file_exists(link));
+}
+
+#[test]
+fn test_link_nonexistent_file() {
+    let file = "test_link_nonexistent_file";
+    let link = "test_link_nonexistent_file_link";
+
+    let result = run(Command::new(PROGNAME).args(&[file, link]));
+    assert_eq!(result.stderr, "link: error: No such file or directory (os error 2)\n");
+    assert!(!result.success);
+    assert!(!file_exists(file));
+    assert!(!file_exists(link));
+}