Fix flaky test.

FD 3 might not be used already.

Author: qwandor

src/lib.rs

@@ -284,7 +284,7 @@ mod tests {
         let file = File::open("testdata/file1.txt").unwrap();
         let file_fd = file.as_raw_fd();
         command.preserved_fds(vec![file_fd]);
-        assert!(file_fd > 3);
+        assert!(file_fd > 2);
 
         let output = command.output().unwrap();
         expect_fds(&output, &[0, 1, 2, 3, file_fd], 0);
@@ -403,7 +403,7 @@ mod tests {
         for entry in dir {
             let entry = entry.unwrap();
             let fd: RawFd = entry.file_name().to_str().unwrap().parse().unwrap();
-            if fd > 3 {
+            if fd > 2 {
                 close(fd).unwrap();
             }
         }