diff --git a/mini-lsm/src/tests/week1_day4.rs b/mini-lsm/src/tests/week1_day4.rs
index 7f0cfd3..efbb100 100644
--- a/mini-lsm/src/tests/week1_day4.rs
+++ b/mini-lsm/src/tests/week1_day4.rs
@@ -55,7 +55,12 @@ fn generate_sst() -> (TempDir, SsTable) {
 
 #[test]
 fn test_sst_build_all() {
-    generate_sst();
+    let (_, sst) = generate_sst();
+    assert_eq!(sst.first_key().as_key_slice(), key_of(0).as_key_slice());
+    assert_eq!(
+        sst.last_key().as_key_slice(),
+        key_of(num_of_keys() - 1).as_key_slice()
+    )
 }
 
 #[test]