feat(tests): day4 tests

Signed-off-by: Alex Chi <iskyzh@gmail.com>

mini-lsm-starter/src/lib.rs

@@ -4,3 +4,6 @@ pub mod lsm_iterator;
 pub mod lsm_storage;
 pub mod mem_table;
 pub mod table;
+
+#[cfg(test)]
+mod tests;