diff --git a/zebra-chain/src/sha256d_writer.rs b/zebra-chain/src/sha256d_writer.rs
index 77dbec20..4e4c14a3 100644
--- a/zebra-chain/src/sha256d_writer.rs
+++ b/zebra-chain/src/sha256d_writer.rs
@@ -40,6 +40,7 @@ mod tests {
     use crate::sha256d_writer::Sha256dWriter;
 
     #[test]
+    // Just checking that `flush()` succeeds without error.
     fn sha256d_flush() {
         let preimage = b"foo bar baz";
         let mut sha_writer = Sha256dWriter::default();