basename: test flag implications, document -z correctly

src/uu/basename/basename.md

@@ -1,7 +1,7 @@
 # basename
 
 ```
-basename NAME [SUFFIX]
+basename [-z] NAME [SUFFIX]
 basename OPTION... NAME...
 ```
 

tests/by-util/test_basename.rs

@@ -201,3 +201,19 @@ fn test_simple_format() {
 fn test_invalid_arg() {
     new_ucmd!().arg("--definitely-invalid").fails().code_is(1);
 }
+
+#[test]
+fn test_zero_does_not_imply_multiple() {
+    new_ucmd!()
+        .args(&["-z", "foo.c", "c"])
+        .succeeds()
+        .stdout_is("foo.\0");
+}
+
+#[test]
+fn test_suffix_implies_multiple() {
+    new_ucmd!()
+        .args(&["-s", ".c", "foo.c", "o.c"])
+        .succeeds()
+        .stdout_is("foo\no\n");
+}