sign: add sanity check for sign API

rust-bindings/rust/tests/sign/mod.rs

@@ -0,0 +1,18 @@
+use gio::NONE_CANCELLABLE;
+use glib::{Bytes, Variant};
+use ostree::{prelude::*, Sign};
+
+#[test]
+fn sign_api_should_work() {
+    let dummy_sign = Sign::get_by_name("dummy").unwrap();
+    assert_eq!(dummy_sign.get_name().unwrap(), "dummy");
+
+    let result = dummy_sign.data(&Bytes::from_static(b"1234"), NONE_CANCELLABLE);
+    assert!(result.is_err());
+
+    let result = dummy_sign.data_verify(&Bytes::from_static(b"1234"), &Variant::from("1234"));
+    assert!(result.is_err());
+
+    let result = Sign::get_by_name("NOPE");
+    assert!(result.is_err());
+}

rust-bindings/rust/tests/tests.rs

@@ -8,4 +8,6 @@ extern crate maplit;
 
 mod functions;
 mod repo;
+#[cfg(feature = "v2020_2")]
+mod sign;
 mod util;