tail: add tests for --debug flag output

Author: ChrisDryden

tests/by-util/test_tail.rs

@@ -5065,3 +5065,42 @@ fn test_follow_stdout_pipe_close() {
     child.close_stdout();
     child.delay(2000).make_assertion().is_not_alive();
 }
+
+#[test]
+fn test_debug_flag_with_polling() {
+    let ts = TestScenario::new(util_name!());
+    let at = &ts.fixtures;
+    at.touch("f");
+
+    let mut child = ts
+        .ucmd()
+        .args(&["--debug", "-f", "--use-polling", "f"])
+        .run_no_wait();
+
+    child.make_assertion_with_delay(500).is_alive();
+    child
+        .kill()
+        .make_assertion()
+        .with_all_output()
+        .stderr_contains("tail: using polling mode");
+}
+
+#[test]
+#[cfg(target_os = "linux")]
+fn test_debug_flag_with_inotify() {
+    let ts = TestScenario::new(util_name!());
+    let at = &ts.fixtures;
+    at.touch("f");
+
+    let mut child = ts
+        .ucmd()
+        .args(&["--debug", "-f", "f"])
+        .run_no_wait();
+
+    child.make_assertion_with_delay(500).is_alive();
+    child
+        .kill()
+        .make_assertion()
+        .with_all_output()
+        .stderr_contains("tail: using notification mode");
+}