test(asserts): Add test for self requires

Add a test that shows that clap doesn't complain when a flag requires
itself.

This test demonstrates existing broken behavior, ideally it should
panic.

It will be fixed in the next commit.

Signed-off-by: Omer Tuchfeld <omer@tuchfeld.dev>

tests/builder/require.rs

@@ -1478,3 +1478,12 @@ For more information, try '--help'.
 ";
     utils::assert_output(cmd, "test --require-first --second", EXPECTED, true);
 }
+
+#[test]
+/// This test demonstrates existing broken behavior, ideally it should panic
+fn requires_self() {
+    let result = Command::new("flag_required")
+        .arg(arg!(-f --flag "some flag").requires("flag"))
+        .try_get_matches_from(vec![""]);
+    assert!(result.is_ok());
+}