Add more tests. Remove unecessary attributes.

test/add.rs

@@ -1,9 +1,18 @@
-#![feature(custom_attribute, rustc_attrs)]
+#![feature(custom_attribute)]
 #![allow(dead_code, unused_attributes)]
 
-#[rustc_mir]
-#[miri_run]
-fn foo() -> i32 {
+#[miri_run(expected = "Int(1)")]
+fn ret() -> i32 {
+    1
+}
+
+#[miri_run(expected = "Int(3)")]
+fn add() -> i32 {
+    1 + 2
+}
+
+#[miri_run(expected = "Int(3)")]
+fn indirect_add() -> i32 {
     let x = 1;
     let y = 2;
     x + y