tests(chore): Rename test files to serial and parallel types

- `test_helper.bats` needs more work than this PR provides to be compatible with parallel tests, so must remain as a serial test for now.
- `spam_bounced.bats` had failures as a serial test, but works well converted to a parallel test in a future commit.

test/tests/serial/permit_docker.bats

@@ -0,0 +1,89 @@
+load 'test_helper/common'
+
+NON_DEFAULT_DOCKER_MAIL_NETWORK_NAME=non-default-docker-mail-network
+setup_file() {
+  docker network create --driver bridge "${NON_DEFAULT_DOCKER_MAIL_NETWORK_NAME}"
+  docker network create --driver bridge "${NON_DEFAULT_DOCKER_MAIL_NETWORK_NAME}2"
+
+  # use two networks (default ("bridge") and our custom network) to recreate problematic test case where PERMIT_DOCKER=host would not help
+  # currently we cannot use --network in `docker run` multiple times, it will just use the last one
+  # instead we need to use create, network connect and start (see https://success.docker.com/article/multiple-docker-networks)
+  local PRIVATE_CONFIG
+
+  PRIVATE_CONFIG=$(duplicate_config_for_container . mail_smtponly_second_network)
+  docker create --name mail_smtponly_second_network \
+    -v "${PRIVATE_CONFIG}":/tmp/docker-mailserver \
+    -v "$(pwd)/test/test-files":/tmp/docker-mailserver-test:ro \
+    -e SMTP_ONLY=1 \
+    -e PERMIT_DOCKER=connected-networks \
+    -e OVERRIDE_HOSTNAME=mail.my-domain.com \
+    --network "${NON_DEFAULT_DOCKER_MAIL_NETWORK_NAME}" \
+    -t "${NAME}"
+
+  docker network connect "${NON_DEFAULT_DOCKER_MAIL_NETWORK_NAME}2" mail_smtponly_second_network
+  docker start mail_smtponly_second_network
+
+  PRIVATE_CONFIG=$(duplicate_config_for_container . mail_smtponly_second_network_sender)
+  docker run -d --name mail_smtponly_second_network_sender \
+    -v "${PRIVATE_CONFIG}":/tmp/docker-mailserver \
+    -v "$(pwd)/test/test-files":/tmp/docker-mailserver-test:ro \
+    -e SMTP_ONLY=1 \
+    -e PERMIT_DOCKER=connected-networks \
+    -e OVERRIDE_HOSTNAME=mail.my-domain.com \
+    --network "${NON_DEFAULT_DOCKER_MAIL_NETWORK_NAME}2" \
+    -t "${NAME}"
+
+  # wait until postfix is up
+  wait_for_smtp_port_in_container mail_smtponly_second_network
+
+  # create another container that enforces authentication even on local connections
+  docker run -d --name mail_smtponly_force_authentication \
+    -v "${PRIVATE_CONFIG}":/tmp/docker-mailserver \
+    -v "$(pwd)/test/test-files":/tmp/docker-mailserver-test:ro \
+    -e SMTP_ONLY=1 \
+    -e PERMIT_DOCKER=none \
+    -e OVERRIDE_HOSTNAME=mail.my-domain.com \
+    -t "${NAME}"
+
+  # wait until postfix is up
+  wait_for_smtp_port_in_container mail_smtponly_force_authentication
+}
+
+teardown_file() {
+  docker logs mail_smtponly_second_network
+  docker rm -f mail_smtponly_second_network mail_smtponly_second_network_sender mail_smtponly_force_authentication
+  docker network rm "${NON_DEFAULT_DOCKER_MAIL_NETWORK_NAME}" "${NON_DEFAULT_DOCKER_MAIL_NETWORK_NAME}2"
+}
+
+@test "checking PERMIT_DOCKER: connected-networks" {
+  IPNET1=$(docker network inspect --format '{{(index .IPAM.Config 0).Subnet}}' non-default-docker-mail-network)
+  IPNET2=$(docker network inspect --format '{{(index .IPAM.Config 0).Subnet}}' non-default-docker-mail-network2)
+  run docker exec mail_smtponly_second_network /bin/sh -c "postconf | grep '^mynetworks ='"
+  assert_output --partial "${IPNET1}"
+  assert_output --partial "${IPNET2}"
+
+  run docker exec mail_smtponly_second_network /bin/sh -c "postconf smtp_host_lookup=no"
+  assert_success
+
+  run docker exec mail_smtponly_second_network /bin/sh -c "/etc/init.d/postfix reload"
+  assert_success
+
+  # we should be able to send from the other container on the second network!
+  run docker exec mail_smtponly_second_network_sender /bin/sh -c "nc mail_smtponly_second_network 25 < /tmp/docker-mailserver-test/email-templates/smtp-only.txt"
+  assert_output --partial "250 2.0.0 Ok: queued as "
+  repeat_until_success_or_timeout 60 run docker exec mail_smtponly_second_network /bin/sh -c 'grep -cE "to=<user2\@external.tld>.*status\=sent" /var/log/mail/mail.log'
+  [[ ${status} -ge 0 ]]
+}
+
+@test "checking PERMIT_DOCKER: none" {
+  run docker exec mail_smtponly_force_authentication /bin/sh -c "postconf smtp_host_lookup=no"
+  assert_success
+
+  run docker exec mail_smtponly_force_authentication /bin/sh -c "/etc/init.d/postfix reload"
+  assert_success
+
+  # the mailserver should require authentication and a protocol error should occur when using TLS
+  run docker exec mail_smtponly_force_authentication /bin/sh -c "nc localhost 25 < /tmp/docker-mailserver-test/email-templates/smtp-only.txt"
+  assert_output --partial "550 5.5.1 Protocol error"
+  [[ ${status} -ge 0 ]]
+}