Add new macro_register test which runs in no_std

tests/macro_register.rs

@@ -0,0 +1,17 @@
+use rhai::plugin::*;
+use rhai::{Engine, EvalAltResult, INT};
+
+
+#[export_fn]
+pub fn add_together(x: INT, y: INT) -> INT {
+    x + y
+}
+
+#[test]
+fn test_exported_fn_register() -> Result<(), Box<EvalAltResult>> {
+    let mut engine = Engine::new();
+    register_exported_fn!(engine, "add_two", add_together);
+    assert_eq!(engine.eval::<INT>("let a = 1; add_two(a, 41)")?, 42);
+
+    Ok(())
+}