dd: Add test to check for dropped writes

(cherry picked from commit 0f7c531)

Author: akretz

tests/by-util/test_dd.rs

@@ -1781,6 +1781,41 @@ fn test_wrong_number_err_msg() {
         .stderr_contains("dd: invalid number: '1kBb555'\n");
 }
 
+#[test]
+#[cfg(all(
+    unix,
+    not(target_os = "macos"),
+    not(target_os = "freebsd"),
+    feature = "printf"
+))]
+fn test_no_dropped_writes() {
+    const BLK_SIZE: usize = 0x4000;
+    const COUNT: usize = 1000;
+    const NUM_BYTES: usize = BLK_SIZE * COUNT;
+
+    let mut reader_command = Command::new(get_tests_binary());
+    let child = reader_command
+        .args(&[
+            "dd",
+            "if=/dev/urandom",
+            &format!("bs={}", BLK_SIZE),
+            &format!("count={}", COUNT),
+        ])
+        .stdout(Stdio::piped())
+        .stderr(Stdio::piped())
+        .env("LC_ALL", "C")
+        .spawn()
+        .unwrap();
+
+    let output = child.wait_with_output().unwrap();
+    assert_eq!(output.stdout.len(), NUM_BYTES);
+    assert!(
+        str::from_utf8(&output.stderr)
+            .unwrap()
+            .contains(&format!("{} bytes", NUM_BYTES))
+    );
+}
+
 #[test]
 #[cfg(any(target_os = "linux", target_os = "android"))]
 fn test_oflag_direct_partial_block() {