ci: run test_bitcoin with DEBUG_LOG_OUT in RUN_UNIT_TESTS_SEQUENTIAL

Resolves bitcoin#28466

ci/test/06_script_b.sh

@@ -167,7 +167,28 @@ if [ "$RUN_UNIT_TESTS" = "true" ]; then
 fi
 
 if [ "$RUN_UNIT_TESTS_SEQUENTIAL" = "true" ]; then
-  bash -c "${TEST_RUNNER_ENV} DIR_UNIT_TEST_DATA=${DIR_UNIT_TEST_DATA} LD_LIBRARY_PATH=${DEPENDS_DIR}/${HOST}/lib ${BASE_OUTDIR}/bin/test_bitcoin --catch_system_errors=no -l test_suite"
+  # The output of test_bitcoin with DEBUG_LOG_OUT is about 80MB. Thus redirect
+  # it to a file and only if errors occur, then extract the relevant snippets
+  # from it - between "Entering test case" and "Leaving test case".
+  LOG="${BASE_BUILD_DIR}/test_bitcoin.log"
+  bash -c "
+    ${TEST_RUNNER_ENV}
+    DIR_UNIT_TEST_DATA=${DIR_UNIT_TEST_DATA}
+    LD_LIBRARY_PATH=${DEPENDS_DIR}/${HOST}/lib
+    if ! ${BASE_OUTDIR}/bin/test_bitcoin --catch_system_errors=no -l test_suite -- DEBUG_LOG_OUT > ${LOG} 2>&1 ; then
+      # find all lines that match 'error: in test_suite/test_case' and extract the test suite and case
+      for t in \$(sed -E -n 's/.*error: in \"(.+\\/.+)\":.*/\\1/p' < ${LOG}) ; do
+        # t is now something like net_tests/v2transport_test
+        test_suite=\${t%/*} # e.g. net_tests
+        test_case=\${t#*/} # e.g. v2transport_test
+        ed -s ${LOG} <<EDCOMMANDS
+          /Entering test suite \"\${test_suite}\"/
+          /Entering test case \"\${test_case}\"/,/Leaving test case \"\${test_case}\"/p
+          q
+EDCOMMANDS
+      done
+    fi
+  "
 fi
 
 if [ "$RUN_FUNCTIONAL_TESTS" = "true" ]; then