tests/chmod: protect umask with a mutex

`test_chmod_ugoa` and `test_chmod_many_options` both change umask, which
is global state. Since tests run concurrently, this might lead to
a situation where one of the tests changes umask to a value that screws
another test's checks. To prevent this, we introduce a mutex that should
be held by any test that changes umask.

Unfortunately, there's no way to hide umask behind this mutex and
enforce its usage: programmers will have to maintain the discipline
themselves.

Cargo.lock

@@ -35,6 +35,7 @@ dependencies = [
  "id 0.0.1",
  "install 0.0.1",
  "kill 0.0.1",
+ "lazy_static 0.2.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "libc 0.2.18 (registry+https://github.com/rust-lang/crates.io-index)",
  "link 0.0.1",
  "ln 0.0.1",

Cargo.toml

@@ -233,6 +233,7 @@ regex="*"
 rand="*"
 tempdir="*"
 unindent="*"
+lazy_static = "*"
 
 [[bin]]
 name = "uutils"

tests/test_chmod.rs

@@ -1,6 +1,7 @@
 use common::util::*;
 use std::fs::{metadata, OpenOptions, set_permissions};
 use std::os::unix::fs::{OpenOptionsExt, PermissionsExt};
+use std::sync::Mutex;
 
 extern crate libc;
 use self::libc::umask;
@@ -9,6 +10,9 @@ use self::libc::umask;
 static TEST_FILE: &'static str = "file";
 static REFERENCE_FILE: &'static str = "reference";
 static REFERENCE_PERMS: u32 = 0o247;
+lazy_static! {
+    static ref UMASK_MUTEX: Mutex<()> = Mutex::new(());
+}
 
 struct TestCase {
     args: Vec<&'static str>,
@@ -70,6 +74,8 @@ fn test_chmod_octal() {
 
 #[test]
 fn test_chmod_ugoa() {
+    let _guard = UMASK_MUTEX.lock();
+
     let last = unsafe {
         umask(0)
     };
@@ -117,6 +123,8 @@ fn test_chmod_ugo_copy() {
 
 #[test]
 fn test_chmod_many_options() {
+    let _guard = UMASK_MUTEX.lock();
+
     let original_umask = unsafe {
         umask(0)
     };

tests/tests.rs

@@ -1,6 +1,9 @@
 #[macro_use]
 mod common;
 
+#[macro_use]
+extern crate lazy_static;
+
 // For conditional compilation
 macro_rules! unix_only {
     ($($fea:expr, $m:ident);+) => {