feat: replace end2end test and add more test

tests/cond_nested.test

@@ -0,0 +1,18 @@
+[expected_return_code]
+42
+
+[code]
+fn main() -> i32 {
+    let x = 5;
+    let y = 10;
+    
+    if x > 0 {
+        if y < 5 {
+            return 1;
+        } else {
+            return 42;
+        }
+    } else {
+        return 2;
+    }
+}