feat: replace end2end test and add more test

tests/cond_else_if.test

@@ -0,0 +1,17 @@
+[expected_return_code]
+7
+
+[code]
+fn main() -> i32 {
+    let n = 4;
+
+    if n == 1 {
+        return 10;
+    } else if n == 2 {
+        return 20;
+    } else if n == 3 {
+        return 30;
+    } else {
+        return 7;
+    }
+}