Add a few more tests for ttyname and getcwd.

Add some tests that would catch the bug fixed in #832.

tests/process/working_directory.rs

@@ -15,6 +15,13 @@ fn test_changing_working_directory() {
     let tmpdir = tmpdir();
 
     let orig_cwd = rustix::process::getcwd(Vec::new()).expect("get the cwd");
+    assert!(orig_cwd.to_str().unwrap().starts_with("/"));
+
+    assert_eq!(
+        orig_cwd.to_str().unwrap(),
+        std::env::current_dir().unwrap().display().to_string(),
+        "rustix's cwd doesn't match std's"
+    );
 
     #[cfg(not(target_os = "fuchsia"))]
     let orig_fd_cwd = rustix::fs::openat(rustix::fs::CWD, ".", OFlags::RDONLY, Mode::empty())

tests/termios/ttyname.rs

@@ -1,3 +1,4 @@
+use rustix::fs::FileTypeExt;
 use rustix::io;
 use rustix::termios::{isatty, ttyname};
 use std::fs::File;
@@ -10,11 +11,13 @@ fn test_ttyname_ok() {
         Err(err) => Err(err).unwrap(),
     };
     if isatty(&file) {
-        assert!(ttyname(&file, Vec::new())
+        let name = ttyname(&file, Vec::new()).unwrap().into_string().unwrap();
+        assert!(name.starts_with("/dev/"));
+        assert!(!name.ends_with("/"));
+        assert!(std::fs::metadata(&name)
             .unwrap()
-            .into_string()
-            .unwrap()
-            .starts_with("/dev/"));
+            .file_type()
+            .is_char_device());
     }
 }