feat: replace end2end test and add more test

tests/cond_assign.test

@@ -0,0 +1,21 @@
+[expected_return_code]
+15
+
+[code]
+fn main() -> i32 {
+    let val = 0;
+
+    if true {
+        val = 10;
+    } else {
+        val = 20;
+    }
+
+    if false {
+        val = val + 100;
+    } else {
+        val = val + 5;
+    }
+    
+    return val;
+}