Use default rust directory structure for tests

tests/internal_fn.rs

@@ -0,0 +1,32 @@
+extern crate rhai;
+
+use rhai::Engine;
+
+#[test]
+fn test_internal_fn() {
+    let mut engine = Engine::new();
+
+    if let Ok(result) = engine.eval::<i64>("fn addme(a, b) { a+b } addme(3, 4)") {
+        assert_eq!(result, 7);
+    } else {
+        assert!(false);
+    }
+
+    if let Ok(result) = engine.eval::<i64>("fn bob() { return 4; 5 } bob()") {
+        assert_eq!(result, 4);
+    } else {
+        assert!(false);
+    }
+}
+
+#[test]
+fn test_big_internal_fn() {
+    let mut engine = Engine::new();
+
+    if let Ok(result) = engine.eval::<i64>("fn mathme(a, b, c, d, e, f) { a - b * c + d * e - f \
+                                            } mathme(100, 5, 2, 9, 6, 32)") {
+        assert_eq!(result, 112);
+    } else {
+        assert!(false);
+    }
+}