More host/target path conversion tests:

- test that the tmpdir Miri tests see is absolute and a directory
- test that current_dir returns an absolute path

src/tools/miri/tests/pass/shims/env/current_dir.rs

@@ -3,8 +3,9 @@ use std::env;
 use std::io::ErrorKind;
 
 fn main() {
-    // Test that `getcwd` is available
+    // Test that `getcwd` is available and an absolute path
     let cwd = env::current_dir().unwrap();
+    assert!(cwd.is_absolute(), "cwd {:?} is not absolute", cwd);
     // Test that changing dir to `..` actually sets the current directory to the parent of `cwd`.
     // The only exception here is if `cwd` is the root directory, then changing directory must
     // keep the current directory equal to `cwd`.

src/tools/miri/tests/pass/shims/fs.rs

@@ -28,6 +28,7 @@ fn main() {
     test_directory();
     test_canonicalize();
     test_from_raw_os_error();
+    test_path_conversion();
 }
 
 fn tmp() -> PathBuf {
@@ -74,6 +75,12 @@ fn prepare_with_content(filename: &str, content: &[u8]) -> PathBuf {
     path
 }
 
+fn test_path_conversion() {
+    let tmp = tmp();
+    assert!(tmp.is_absolute(), "{:?} is not absolute", tmp);
+    assert!(tmp.is_dir(), "{:?} is not a directory", tmp);
+}
+
 fn test_file() {
     let bytes = b"Hello, World!\n";
     let path = prepare("miri_test_fs_file.txt");