echo: Add more tests

tests/by-util/test_echo.rs

@@ -19,6 +19,11 @@ fn test_no_trailing_newline() {
     new_ucmd!().arg("-n").arg("hi").succeeds().stdout_only("hi");
 }
 
+#[test]
+fn test_empty_args() {
+    new_ucmd!().succeeds().stdout_only("\n");
+}
+
 #[test]
 fn test_escape_alert() {
     new_ucmd!()
@@ -523,12 +528,30 @@ fn full_version_argument() {
         .stdout_matches(&Regex::new(r"^echo \(uutils coreutils\) (\d+\.\d+\.\d+)\n$").unwrap());
 }
 
+#[test]
+fn multiple_version_argument() {
+    new_ucmd!()
+        .arg("--version")
+        .arg("--version")
+        .succeeds()
+        .stdout_is("--version --version\n");
+}
+
 #[test]
 fn full_help_argument() {
     assert_ne!(new_ucmd!().arg("--help").succeeds().stdout(), b"--help\n");
     assert_ne!(new_ucmd!().arg("--help").succeeds().stdout(), b"--help"); // This one is just in case.
 }
 
+#[test]
+fn multiple_help_argument() {
+    new_ucmd!()
+        .arg("--help")
+        .arg("--help")
+        .succeeds()
+        .stdout_is("--help --help\n");
+}
+
 #[test]
 fn multibyte_escape_unicode() {
     // spell-checker:disable-next-line