Without the patch, the gets from the non-blocking socket $s1 returns an empty string here, instead of the bye written into it from the other side:

--- tests/tlsIO.test 2020-10-12 16:39:22.000000000 -0400
+++ tests/tlsIO.test 2023-11-19 20:33:44.077356000 -0500
@@ -1106,4 +1106,5 @@
     # need update to complete TLS handshake in-process
     update
+    fconfigure $s1 -blocking 1
     set z [gets $s1]
     close $s