separated tests for mergability

src/tests/mismatched_op.rs

@@ -0,0 +1,11 @@
+use engine::{Engine, EvalAltResult};
+
+#[test]
+fn test_mismatched_op() {
+    let mut engine = Engine::new();
+
+    match engine.eval::<i64>("60 + \"hello\"") {
+        Err(EvalAltResult::ErrorFunctionArgMismatch) => (),
+        _ => assert!(false),
+    }
+}