tests/install: add stdin test using fd from /proc directly

Author: DaringCuteSeal

tests/by-util/test_install.rs

@@ -1751,3 +1751,19 @@ fn test_install_from_fifo() {
     assert!(s.fixtures.file_exists(target_name));
     assert_eq!(s.fixtures.read(target_name), test_string);
 }
+
+#[test]
+#[cfg(unix)]
+fn test_install_from_stdin() {
+    let (at, mut ucmd) = at_and_ucmd!();
+    let target = "target";
+    let test_string = "Hello, World!\n";
+
+    ucmd.arg("/proc/self/fd/0")
+        .arg(target)
+        .pipe_in(test_string)
+        .succeeds();
+
+    assert!(at.file_exists(target));
+    assert_eq!(at.read(target), test_string);
+}