Add more clap tests.

Bug: 260823636
Test: atest compos_verify.test fd_server.test initrd_bootconfig.test composd_cmd.test
Change-Id: I7fe3fbf5b8c349618ccdef2f096b77737eabed42
diff --git a/authfs/fd_server/src/main.rs b/authfs/fd_server/src/main.rs
index 9d97423..f91ebec 100644
--- a/authfs/fd_server/src/main.rs
+++ b/authfs/fd_server/src/main.rs
@@ -148,3 +148,15 @@
     server.join();
     Ok(())
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use clap::CommandFactory;
+
+    #[test]
+    fn verify_args() {
+        // Check that the command parsing has been configured in a valid way.
+        Args::command().debug_assert();
+    }
+}