OpenSSL::SSL::SSLContext#cert_store= uses SSL_CTX_set_cert_store(). The store is used for verifying peer certificates and for building certificate chains to be sent to the peer if there is no chain explicitly provided by SSLContext#extra_chain_cert=. Do not specify it in the common test helper start_server, as most callers do not require either function. Instead, update individual test cases that use client certificates to explicitly specify it in ctx_proc. A more direct test case is added to verify the latter function. https://.com/ruby/openssl/commit/9daecee615