tail: Add test for tail -f.

tests/common/util.rs

@@ -3,7 +3,7 @@
 extern crate tempdir;
 
 use std::env;
-use std::fs::{self, File};
+use std::fs::{self, File, OpenOptions};
 use std::io::{Read, Write, Result};
 use std::ops::{Deref, DerefMut};
 #[cfg(unix)]
@@ -16,6 +16,8 @@ use std::str::from_utf8;
 use std::ffi::OsStr;
 use self::tempdir::TempDir;
 use std::rc::Rc;
+use std::thread::sleep;
+use std::time::Duration;
 
 #[cfg(windows)]
 static PROGNAME: &'static str = "target\\debug\\uutils.exe";
@@ -242,6 +244,12 @@ impl AtPath {
         let _ = f.write(contents.as_bytes());
     }
 
+    pub fn append(&self, name: &str, contents: &str) {
+        log_info("open(append)", self.plus_as_string(name));
+        let mut f = OpenOptions::new().append(true).open(self.plus(name)).unwrap();
+        let _ = f.write(contents.as_bytes());
+    }
+
     pub fn mkdir(&self, dir: &str) {
         log_info("mkdir", self.plus_as_string(dir));
         fs::create_dir(&self.plus(dir)).unwrap();
@@ -544,6 +552,14 @@ impl UCommand {
     }
 }
 
+pub fn read_size(child: &mut Child, size: usize) -> String {
+    let mut output = Vec::new();
+    output.resize(size, 0);
+    sleep(Duration::from_millis(100));
+    child.stdout.as_mut().unwrap().read(output.as_mut_slice()).unwrap();
+    String::from_utf8(output).unwrap()
+}
+
 // returns a testSet and a ucommand initialized to the utility binary
 // operating in the fixtures directory with a cleared environment
 pub fn testset_and_ucommand(utilname: &str) -> (TestSet, UCommand) {

tests/tail.rs

@@ -1,6 +1,7 @@
 extern crate uu_tail;
 use uu_tail::parse_size;
 
+use std::io::Read;
 use std::io::Write;
 
 #[macro_use]
@@ -41,6 +42,24 @@ fn test_null_default() {
     assert_eq!(result.stdout, at.read("foobar_with_null_default.expected"));
 }
 
+#[test]
+fn test_follow() {
+    let (at, mut ucmd) = testing(UTIL_NAME);
+
+    let mut child = ucmd.arg("-f").arg(FOOBAR_TXT).run_no_wait();
+
+    let expected = at.read("foobar_single_default.expected");
+    assert_eq!(read_size(&mut child, expected.len()), expected);
+
+    // We write in a temporary copy of foobar.txt
+    let expected = "line1\nline2\n";
+    at.append(FOOBAR_TXT, expected);
+
+    assert_eq!(read_size(&mut child, expected.len()), expected);
+
+    child.kill().unwrap();
+}
+
 #[test]
 fn test_single_big_args() {
     const FILE: &'static str = "single_big_args.txt";