logname: add help and output format tests (#11118)

* logname: add help and output format tests

tests/by-util/test_logname.rs

@@ -2,6 +2,7 @@
 //
 // For the full copyright and license information, please view the LICENSE
 // file that was distributed with this source code.
+use regex::Regex;
 use std::env;
 use uutests::new_ucmd;
 use uutests::util::is_ci;
@@ -29,3 +30,27 @@ fn test_normal() {
     result.success();
     assert!(!result.stdout_str().trim().is_empty());
 }
+
+#[test]
+fn test_help() {
+    new_ucmd!()
+        .arg("--help")
+        .succeeds()
+        .stdout_contains("Print user's login name");
+}
+
+#[test]
+fn test_output_format() {
+    let result = new_ucmd!().run();
+    if (is_ci() || uucore::os::is_wsl()) && result.stderr_str().contains("no login name") {
+        return;
+    }
+    result.success();
+    assert!(
+        Regex::new(r"^\w+\n$")
+            .unwrap()
+            .is_match(result.stdout_str()),
+        "unexpected logname output: {:?}",
+        result.stdout_str()
+    );
+}