new filters for searching logs with MID

test/helper/log_and_filtering.bash

@@ -58,3 +58,40 @@ function _service_log_should_contain_string() {
   _filter_service_log "${SERVICE}" "${STRING}"
   assert_success
 }
+
+# Filters the mail log according to MID (Message-ID) and prints lines
+# of the mail log that fit Postfix's queue ID for the given message ID.
+#
+# @param ${1} = message ID part before '@'
+function _print_mail_log_of_queue_id_from_mid() {
+  # The unique ID Postfix (and other services) use may be different in length
+  # on different systems. Hence, we use a range to safely capture it.
+  local QUEUE_ID_REGEX='[A-Z0-9]{9,12}'
+
+  local MID=$(__construct_mid "${1:?Left-hand side of MID missing}")
+  shift 1
+
+  _wait_for_empty_mail_queue_in_container
+
+  QUEUE_ID=$(_exec_in_container tac /var/log/mail.log                    \
+    | grep -E "postfix/cleanup.*: ${QUEUE_ID_REGEX}:.*message-id=${MID}" \
+    | grep -E --only-matching --max-count 1 "${QUEUE_ID_REGEX}" || :)
+
+  # We perform plausibility checks on the IDs.
+  assert_not_equal "${QUEUE_ID}" ''
+  run echo "${QUEUE_ID}"
+  assert_line --regexp "^${QUEUE_ID_REGEX}$"
+
+  _filter_service_log 'mail' "${QUEUE_ID}"
+}
+
+# Filters the mail log according to MID (Message-ID) and prints lines
+# of the mail log that fit lines with the pattern `msgid=${1}@dms-test`.
+#
+# @param ${1} = message ID part before '@'
+function _print_mail_log_for_msgid() {
+  local MID=$(__construct_mid "${1:?Left-hand side of MID missing}")
+  shift 1
+
+  _filter_service_log 'mail' "msgid=${MID}"
+}