Update basis_spec.txt

spec/basis_spec.txt

diff --git a/spec/basis_spec.txt b/spec/basis_spec.txt
index 9134d72..b72a29a 100644
--- a/spec/basis_spec.txt
+++ b/spec/basis_spec.txt
@@ -800,7 +800,7 @@
             // Compute the history buffer index
             int history_buf_index = selector_sym - (int)selectors.size();
 
-            if (history_buf_index < selector_history_buf.size());
+            assert(history_buf_index < selector_history_buf.size());
 
             // Access the history buffer
             selector_index = selector_history_buf[history_buf_index];