diff --git a/test/mail_dhparams_manual_not_one_dir.bats b/test/mail_dhparams_manual_not_one_dir.bats
index 2277c2f5..f2072a8b 100644
--- a/test/mail_dhparams_manual_not_one_dir.bats
+++ b/test/mail_dhparams_manual_not_one_dir.bats
@@ -23,10 +23,10 @@ function teardown() {
 function setup_file() {
     private_config=$(duplicate_config_for_container .)
     # copy the custom DHE params in local config
-    cp "`pwd`/test/test-files/ssl/custom-dhe-params.pem" "$private_config/dhparams.pem"
+    cp "`pwd`/test/test-files/ssl/custom-dhe-params.pem" "${private_config}/dhparams.pem"
 
     docker run -d --name mail_manual_dhparams_not_one_dir \
-		-v "$private_config":/tmp/docker-mailserver \
+		-v "${private_config}":/tmp/docker-mailserver \
 		-v "`pwd`/test/test-files":/tmp/docker-mailserver-test:ro \
 		-e DMS_DEBUG=0 \
 		-e ONE_DIR=0 \
diff --git a/test/mail_ssl_letsencrypt.bats b/test/mail_ssl_letsencrypt.bats
index cb826208..c6e74a91 100644
--- a/test/mail_ssl_letsencrypt.bats
+++ b/test/mail_ssl_letsencrypt.bats
@@ -11,9 +11,9 @@ function teardown() {
 function setup_file() {
   private_config="$(duplicate_config_for_container . mail_lets_domain)"
   docker run -d --name mail_lets_domain \
-  -v "$private_config":/tmp/docker-mailserver \
+  -v "${private_config}":/tmp/docker-mailserver \
   -v "`pwd`/test/test-files":/tmp/docker-mailserver-test:ro \
-  -v "$private_config/letsencrypt/my-domain.com":/etc/letsencrypt/live/my-domain.com \
+  -v "${private_config}/letsencrypt/my-domain.com":/etc/letsencrypt/live/my-domain.com \
   -e DMS_DEBUG=0 \
   -e SSL_TYPE=letsencrypt \
   -h mail.my-domain.com -t ${NAME}
@@ -21,9 +21,9 @@ function setup_file() {
 
   private_config="$(duplicate_config_for_container . mail_lets_hostname)"
   docker run -d --name mail_lets_hostname \
-  -v "$private_config":/tmp/docker-mailserver \
+  -v "${private_config}":/tmp/docker-mailserver \
   -v "`pwd`/test/test-files":/tmp/docker-mailserver-test:ro \
-  -v "$private_config/letsencrypt/mail.my-domain.com":/etc/letsencrypt/live/mail.my-domain.com \
+  -v "${private_config}/letsencrypt/mail.my-domain.com":/etc/letsencrypt/live/mail.my-domain.com \
   -e DMS_DEBUG=0 \
   -e SSL_TYPE=letsencrypt \
   -h mail.my-domain.com -t ${NAME}
@@ -32,8 +32,8 @@ function setup_file() {
   private_config="$(duplicate_config_for_container . mail_lets_acme_json)"
   cp "$(private_config_path mail_lets_acme_json)/letsencrypt/acme.json" "$(private_config_path mail_lets_acme_json)/acme.json"
   docker run -d --name mail_lets_acme_json \
-    -v "$private_config":/tmp/docker-mailserver \
-    -v "$private_config/acme.json":/etc/letsencrypt/acme.json:ro \
+    -v "${private_config}":/tmp/docker-mailserver \
+    -v "${private_config}/acme.json":/etc/letsencrypt/acme.json:ro \
     -v "`pwd`/test/test-files":/tmp/docker-mailserver-test:ro \
     -e DMS_DEBUG=0 \
     -e SSL_TYPE=letsencrypt \
diff --git a/test/test_helper/common.bash b/test/test_helper/common.bash
index e6c03ba0..95800011 100644
--- a/test/test_helper/common.bash
+++ b/test/test_helper/common.bash
@@ -7,107 +7,107 @@ NAME=tvial/docker-mailserver:testing
 TEST_TIMEOUT_IN_SECONDS=${TEST_TIMEOUT_IN_SECONDS-120}
 NUMBER_OF_LOG_LINES=${NUMBER_OF_LOG_LINES-10}
 
-# @param $1 timeout
+# @param ${1} timeout
 # @param --fatal-test <command eval string> additional test whose failure aborts immediately
 # @param ... test to run
 function repeat_until_success_or_timeout {
     local fatal_failure_test_command
-    if [[ "$1" == "--fatal-test" ]]; then
-        fatal_failure_test_command="$2"
+    if [[ "${1}" == "--fatal-test" ]]; then
+        fatal_failure_test_command="${2}"
         shift 2
     fi
-    if ! [[ "$1" =~ ^[0-9]+$ ]]; then
-        echo "First parameter for timeout must be an integer, recieved \"$1\""
+    if ! [[ "${1}" =~ ^[0-9]+$ ]]; then
+        echo "First parameter for timeout must be an integer, recieved \"${1}\""
         return 1
     fi
-    TIMEOUT=$1
-    STARTTIME=$SECONDS
+    local TIMEOUT=${1}
+    local STARTTIME=${SECONDS}
     shift 1
-    until "$@"
+    until "${@}"
     do
-        if [[ -n "$fatal_failure_test_command" ]] && ! eval "$fatal_failure_test_command"; then
-            echo "\`$fatal_failure_test_command\` failed, early aborting repeat_until_success of \`$*\`" >&2
+        if [[ -n "${fatal_failure_test_command}" ]] && ! eval "${fatal_failure_test_command}"; then
+            echo "\`${fatal_failure_test_command}\` failed, early aborting repeat_until_success of \`${*}\`" >&2
             exit 1
         fi
         sleep 5
-        if [[ $(( SECONDS - STARTTIME )) -gt $TIMEOUT ]]; then
-            echo "Timed out on command: $*" >&2
+        if [[ $(( SECONDS - STARTTIME )) -gt ${TIMEOUT} ]]; then
+            echo "Timed out on command: ${*}" >&2
             return 1
         fi
     done
 }
 
 # like repeat_until_success_or_timeout but with wrapping the command to run into `run` for later bats consumption
-# @param $1 timeout
+# @param ${1} timeout
 # @param ... test command to run
 function run_until_success_or_timeout {
-    if ! [[ "$1" =~ ^[0-9]+$ ]]; then
-        echo "First parameter for timeout must be an integer, recieved \"$1\""
+    if ! [[ "${1}" =~ ^[0-9]+$ ]]; then
+        echo "First parameter for timeout must be an integer, recieved \"${1}\""
         return 1
     fi
-    TIMEOUT=$1
-    STARTTIME=$SECONDS
+    local TIMEOUT=${1}
+    local STARTTIME=${SECONDS}
     shift 1
-    until run "$@" && [[ $status -eq 0 ]]
+    until run "${@}" && [[ ${status} -eq 0 ]]
     do
         sleep 1
-        if [[ $(( SECONDS - STARTTIME )) -gt $TIMEOUT ]]; then
-            echo "Timed out on command: $*" >&2
+        if [[ $(( SECONDS - STARTTIME )) -gt ${TIMEOUT} ]]; then
+            echo "Timed out on command: ${*}" >&2
             return 1
         fi
     done
 }
 
-# @param $1 timeout
-# @param $2 container name
+# @param ${1} timeout
+# @param ${2} container name
 # @param ... test command for container
 function repeat_in_container_until_success_or_timeout() {
-    timeout="$1"
-    container_name="$2"
+    local TIMEOUT="${1}"
+    local CONTAINER_NAME="${2}"
     shift 2
-    repeat_until_success_or_timeout --fatal-test "container_is_running $container_name" "$timeout" docker exec "$container_name" "$@"
+    repeat_until_success_or_timeout --fatal-test "container_is_running ${CONTAINER_NAME}" "${TIMEOUT}" docker exec "${CONTAINER_NAME}" "${@}"
 }
 
 function container_is_running() {
-    [[ "$(docker inspect -f '{{.State.Running}}' "$1")" == "true" ]]
+    [[ "$(docker inspect -f '{{.State.Running}}' "${1}")" == "true" ]]
 }
 
-# @param $1 port
-# @param $2 container name
+# @param ${1} port
+# @param ${2} container name
 function wait_for_tcp_port_in_container() {
-    repeat_until_success_or_timeout --fatal-test "container_is_running $2" "$TEST_TIMEOUT_IN_SECONDS" docker exec $2 /bin/sh -c "nc -z 0.0.0.0 $1"
+    repeat_until_success_or_timeout --fatal-test "container_is_running ${2}" "${TEST_TIMEOUT_IN_SECONDS}" docker exec ${2} /bin/sh -c "nc -z 0.0.0.0 ${1}"
 }
 
-# @param $1 name of the postfix container
+# @param ${1} name of the postfix container
 function wait_for_smtp_port_in_container() {
-    wait_for_tcp_port_in_container 25 "$1"
+    wait_for_tcp_port_in_container 25 "${1}"
 }
 
-# @param $1 name of the postfix container
+# @param ${1} name of the postfix container
 function wait_for_amavis_port_in_container() {
-    wait_for_tcp_port_in_container 10024 "$1"
+    wait_for_tcp_port_in_container 10024 "${1}"
 }
 
-# @param $1 name of the postfix container
+# @param ${1} name of the postfix container
 function wait_for_finished_setup_in_container() {
     local status=0
-    repeat_until_success_or_timeout --fatal-test "container_is_running $1" "$TEST_TIMEOUT_IN_SECONDS" sh -c "docker logs $1 | grep 'is up and running'" || status=1
-    if [[ $status -eq 1 ]]; then
-        echo "Last $NUMBER_OF_LOG_LINES lines of container \`$1\`'s log"
-        docker logs "$1" | tail -n "$NUMBER_OF_LOG_LINES"
+    repeat_until_success_or_timeout --fatal-test "container_is_running ${1}" "${TEST_TIMEOUT_IN_SECONDS}" sh -c "docker logs ${1} | grep 'is up and running'" || status=1
+    if [[ ${status} -eq 1 ]]; then
+        echo "Last ${NUMBER_OF_LOG_LINES} lines of container \`${1}\`'s log"
+        docker logs "${1}" | tail -n "${NUMBER_OF_LOG_LINES}"
     fi
-    return $status
+    return ${status}
 }
 
-SETUP_FILE_MARKER="$BATS_TMPDIR/$(basename "$BATS_TEST_FILENAME").setup_file"
+SETUP_FILE_MARKER="${BATS_TMPDIR}/$(basename "${BATS_TEST_FILENAME}").setup_file"
 
 function native_setup_teardown_file_support() {
-    VERSION_REGEX='([0-9]+)\.([0-9]+)\.([0-9]+)'
+    local VERSION_REGEX='([0-9]+)\.([0-9]+)\.([0-9]+)'
     # bats versions that support setup_file out of the box don't need this
-    if [[ "$BATS_VERSION" =~ $VERSION_REGEX ]]; then
+    if [[ "${BATS_VERSION}" =~ ${VERSION_REGEX} ]]; then
         numeric_version=$(( (BASH_REMATCH[1] * 100 + BASH_REMATCH[2]) * 100 + BASH_REMATCH[3] ))
-        if [[ $numeric_version -ge 10201 ]]; then
-            if [ "$BATS_TEST_NAME" == 'test_first' ]; then
+        if [[ ${numeric_version} -ge 10201 ]]; then
+            if [ "${BATS_TEST_NAME}" == 'test_first' ]; then
                 skip 'This version natively supports setup/teardown_file'
             fi
             return 0
@@ -119,15 +119,15 @@ function native_setup_teardown_file_support() {
 # use in setup() in conjunction with a `@test "first" {}` to trigger setup_file reliably
 function run_setup_file_if_necessary() {
     native_setup_teardown_file_support && return 0
-    if [ "$BATS_TEST_NAME" == 'test_first' ]; then
+    if [ "${BATS_TEST_NAME}" == 'test_first' ]; then
         # prevent old markers from marking success or get an error if we cannot remove due to permissions
-        rm -f "$SETUP_FILE_MARKER"
+        rm -f "${SETUP_FILE_MARKER}"
 
         setup_file
 
-        touch "$SETUP_FILE_MARKER"
+        touch "${SETUP_FILE_MARKER}"
     else
-        if [ ! -f "$SETUP_FILE_MARKER" ]; then
+        if [ ! -f "${SETUP_FILE_MARKER}" ]; then
             skip "setup_file failed"
             return 1
         fi
@@ -137,52 +137,52 @@ function run_setup_file_if_necessary() {
 # use in teardown() in conjunction with a `@test "last" {}` to trigger teardown_file reliably
 function run_teardown_file_if_necessary() {
     native_setup_teardown_file_support && return 0
-    if [ "$BATS_TEST_NAME" == 'test_last' ]; then
+    if [ "${BATS_TEST_NAME}" == 'test_last' ]; then
         # cleanup setup file marker
-        rm -f "$SETUP_FILE_MARKER"
+        rm -f "${SETUP_FILE_MARKER}"
         teardown_file
     fi
 }
 
 # get the private config path for the given container or test file, if no container name was given
 function private_config_path() {
-    echo "$PWD/test/duplicate_configs/${1:-$(basename "$BATS_TEST_FILENAME")}"
+    echo "${PWD}/test/duplicate_configs/${1:-$(basename "${BATS_TEST_FILENAME}")}"
 }
 
-# @param $1 relative source in test/config folder
-# @param $2 (optional) container name, defaults to $BATS_TEST_FILENAME
+# @param ${1} relative source in test/config folder
+# @param ${2} (optional) container name, defaults to ${BATS_TEST_FILENAME}
 # @return path to the folder where the config is duplicated
 function duplicate_config_for_container() {
-    output="$(private_config_path "$2")"
-    rm -rf "${output:?}/" # cleanup
-    mkdir -p "$output"
-    cp -r "$PWD/test/config/${1:?}/." "$output"
-    echo "$output"
+    local OUTPUT_FOLDER="$(private_config_path "${2}")"
+    rm -rf "${OUTPUT_FOLDER:?}/" # cleanup
+    mkdir -p "${OUTPUT_FOLDER}"
+    cp -r "${PWD}/test/config/${1:?}/." "${OUTPUT_FOLDER}"
+    echo "${OUTPUT_FOLDER}"
 }
 
 function container_has_service_running() {
-    containerName="$1"
-    serviceName="$2"
-    docker exec "$containerName" /usr/bin/supervisorctl status "$serviceName" | grep RUNNING >/dev/null
+    local CONTAINER_NAME="${1}"
+    local SERVICE_NAME="${2}"
+    docker exec "${CONTAINER_NAME}" /usr/bin/supervisorctl status "${SERVICE_NAME}" | grep RUNNING >/dev/null
 }
 
 function wait_for_service() {
-    containerName="$1"
-    serviceName="$2"
-    repeat_until_success_or_timeout --fatal-test "container_is_running $containerName" 60 \
-        container_has_service_running "$containerName" "$serviceName"
+    local CONTAINER_NAME="${1}"
+    local SERVICE_NAME="${2}"
+    repeat_until_success_or_timeout --fatal-test "container_is_running ${CONTAINER_NAME}" 60 \
+        container_has_service_running "${CONTAINER_NAME}" "${SERVICE_NAME}"
 }
 
 function count_processed_changes() {
-    containerName=$1
-    docker exec "$containerName" cat /var/log/supervisor/changedetector.log | grep "Change detected" -c \
-        || [[ $? == 1 ]] # don't error when no matches were found
+    local CONTAINER_NAME=${1}
+    docker exec "${CONTAINER_NAME}" cat /var/log/supervisor/changedetector.log | grep "Change detected" -c \
+        || [[ ${?} == 1 ]] # don't error when no matches were found
 }
 
 
 function wait_for_changes_to_be_detected_in_container() {
-    containerName="$1"
-    timeout=${TEST_TIMEOUT_IN_SECONDS}
-    repeat_in_container_until_success_or_timeout "$timeout" "$containerName" \
-        bash -c 'source /usr/local/bin/helper_functions.sh; cmp --silent -- <(_monitored_files_checksums) "$CHKSUM_FILE"  >/dev/null'
+    local CONTAINER_NAME="${1}"
+    local TIMEOUT=${TEST_TIMEOUT_IN_SECONDS}
+    repeat_in_container_until_success_or_timeout "${TIMEOUT}" "${CONTAINER_NAME}" \
+        bash -c 'source /usr/local/bin/helper_functions.sh; cmp --silent -- <(_monitored_files_checksums) "${CHKSUM_FILE}"  >/dev/null'
 }
diff --git a/test/tests.bats b/test/tests.bats
index 4700660d..88e1793a 100644
--- a/test/tests.bats
+++ b/test/tests.bats
@@ -8,9 +8,9 @@ setup() {
 
 setup_file() {
   private_config="$(duplicate_config_for_container . mail)"
-  mv "$private_config/user-patches/user-patches.sh" "$private_config/user-patches.sh"
+  mv "${private_config}/user-patches/user-patches.sh" "${private_config}/user-patches.sh"
   docker run --rm -d --name mail \
-		-v "$private_config":/tmp/docker-mailserver \
+		-v "${private_config}":/tmp/docker-mailserver \
 		-v "`pwd`/test/test-files":/tmp/docker-mailserver-test:ro \
 		-v "`pwd`/test/onedir":/var/mail-state \
 		-e ENABLE_CLAMAV=1 \
@@ -34,11 +34,11 @@ setup_file() {
   wait_for_finished_setup_in_container mail
   
   # generate accounts after container has been started
-  docker run --rm -e MAIL_USER=added@localhost.localdomain -e MAIL_PASS=mypassword -t ${NAME} /bin/sh -c 'echo "$MAIL_USER|$(doveadm pw -s SHA512-CRYPT -u $MAIL_USER -p $MAIL_PASS)"' >> "$private_config/postfix-accounts.cf"
+  docker run --rm -e MAIL_USER=added@localhost.localdomain -e MAIL_PASS=mypassword -t ${NAME} /bin/sh -c 'echo "${MAIL_USER}|$(doveadm pw -s SHA512-CRYPT -u ${MAIL_USER} -p ${MAIL_PASS})"' >> "${private_config}/postfix-accounts.cf"
   docker exec mail addmailuser pass@localhost.localdomain 'may be \a `p^a.*ssword'
   
   # setup sieve
-	docker cp "$private_config/sieve/dovecot.sieve" mail:/var/mail/localhost.localdomain/user1/.dovecot.sieve
+	docker cp "${private_config}/sieve/dovecot.sieve" mail:/var/mail/localhost.localdomain/user1/.dovecot.sieve
 
   # this relies on the checksum file beeing updated after all changes have been applied
   wait_for_changes_to_be_detected_in_container mail
@@ -459,19 +459,19 @@ EOF
 @test "checking opendkim: generator creates default keys size" {
     private_config="$(duplicate_config_for_container . mail_default_key_size)"
     # Prepare default key size 2048
-    rm -rf "$private_config/keyDefault"
-    mkdir -p "$private_config/keyDefault"
+    rm -rf "${private_config}/keyDefault"
+    mkdir -p "${private_config}/keyDefault"
 
     run docker run --rm \
-      -v "$private_config/keyDefault/":/tmp/docker-mailserver/ \
-      -v "$private_config/postfix-accounts.cf":/tmp/docker-mailserver/postfix-accounts.cf \
-      -v "$private_config/postfix-virtual.cf":/tmp/docker-mailserver/postfix-virtual.cf \
+      -v "${private_config}/keyDefault/":/tmp/docker-mailserver/ \
+      -v "${private_config}/postfix-accounts.cf":/tmp/docker-mailserver/postfix-accounts.cf \
+      -v "${private_config}/postfix-virtual.cf":/tmp/docker-mailserver/postfix-virtual.cf \
       `docker inspect --format '{{ .Config.Image }}' mail` /bin/sh -c 'generate-dkim-config | wc -l'
     assert_success
     assert_output 6
 
   run docker run --rm \
-    -v "$private_config/keyDefault/opendkim":/etc/opendkim \
+    -v "${private_config}/keyDefault/opendkim":/etc/opendkim \
     `docker inspect --format '{{ .Config.Image }}' mail` \
     /bin/sh -c 'stat -c%s /etc/opendkim/keys/localhost.localdomain/mail.txt'
 
@@ -485,18 +485,18 @@ EOF
 @test "checking opendkim: generator creates key size 2048" {
     private_config="$(duplicate_config_for_container . mail_key_size_2048)"
     # Prepare set key size 2048
-    rm -rf "$private_config/key2048"
-    mkdir -p "$private_config/config/key2048"
+    rm -rf "${private_config}/key2048"
+    mkdir -p "${private_config}/config/key2048"
     run docker run --rm \
-      -v "$private_config/key2048/":/tmp/docker-mailserver/ \
-      -v "$private_config/postfix-accounts.cf":/tmp/docker-mailserver/postfix-accounts.cf \
-      -v "$private_config/postfix-virtual.cf":/tmp/docker-mailserver/postfix-virtual.cf \
+      -v "${private_config}/key2048/":/tmp/docker-mailserver/ \
+      -v "${private_config}/postfix-accounts.cf":/tmp/docker-mailserver/postfix-accounts.cf \
+      -v "${private_config}/postfix-virtual.cf":/tmp/docker-mailserver/postfix-virtual.cf \
       `docker inspect --format '{{ .Config.Image }}' mail` /bin/sh -c 'generate-dkim-config 2048 | wc -l'
     assert_success
     assert_output 6
 
   run docker run --rm \
-    -v "$private_config/key2048/opendkim":/etc/opendkim \
+    -v "${private_config}/key2048/opendkim":/etc/opendkim \
     `docker inspect --format '{{ .Config.Image }}' mail` \
     /bin/sh -c 'stat -c%s /etc/opendkim/keys/localhost.localdomain/mail.txt'
 
@@ -510,18 +510,18 @@ EOF
 @test "checking opendkim: generator creates key size 1024" {
     private_config="$(duplicate_config_for_container . mail_key_size_1024)"
     # Prepare set key size 1024
-    rm -rf "$private_config/key1024"
-    mkdir -p "$private_config/key1024"
+    rm -rf "${private_config}/key1024"
+    mkdir -p "${private_config}/key1024"
     run docker run --rm \
-      -v "$private_config/key1024/":/tmp/docker-mailserver/ \
-      -v "$private_config/postfix-accounts.cf":/tmp/docker-mailserver/postfix-accounts.cf \
-      -v "$private_config/postfix-virtual.cf":/tmp/docker-mailserver/postfix-virtual.cf \
+      -v "${private_config}/key1024/":/tmp/docker-mailserver/ \
+      -v "${private_config}/postfix-accounts.cf":/tmp/docker-mailserver/postfix-accounts.cf \
+      -v "${private_config}/postfix-virtual.cf":/tmp/docker-mailserver/postfix-virtual.cf \
       `docker inspect --format '{{ .Config.Image }}' mail` /bin/sh -c 'generate-dkim-config 1024 | wc -l'
     assert_success
     assert_output 6
 
   run docker run --rm \
-    -v "$private_config/key1024/opendkim":/etc/opendkim \
+    -v "${private_config}/key1024/opendkim":/etc/opendkim \
     `docker inspect --format '{{ .Config.Image }}' mail` \
     /bin/sh -c 'stat -c%s /etc/opendkim/keys/localhost.localdomain/mail.txt'
 
@@ -531,30 +531,30 @@ EOF
 
 @test "checking opendkim: generator creates keys, tables and TrustedHosts" {
   private_config="$(duplicate_config_for_container . mail_dkim_generator_creates_keys_tables_TrustedHosts)"
-  rm -rf "$private_config/empty"
-  mkdir -p "$private_config/empty"
+  rm -rf "${private_config}/empty"
+  mkdir -p "${private_config}/empty"
   run docker run --rm \
-    -v "$private_config/empty/":/tmp/docker-mailserver/ \
-    -v "$private_config/postfix-accounts.cf":/tmp/docker-mailserver/postfix-accounts.cf \
-    -v "$private_config/postfix-virtual.cf":/tmp/docker-mailserver/postfix-virtual.cf \
+    -v "${private_config}/empty/":/tmp/docker-mailserver/ \
+    -v "${private_config}/postfix-accounts.cf":/tmp/docker-mailserver/postfix-accounts.cf \
+    -v "${private_config}/postfix-virtual.cf":/tmp/docker-mailserver/postfix-virtual.cf \
     `docker inspect --format '{{ .Config.Image }}' mail` /bin/sh -c 'generate-dkim-config | wc -l'
   assert_success
   assert_output 6
   # Check keys for localhost.localdomain
   run docker run --rm \
-    -v "$private_config/empty/opendkim":/etc/opendkim \
+    -v "${private_config}/empty/opendkim":/etc/opendkim \
     `docker inspect --format '{{ .Config.Image }}' mail` /bin/sh -c 'ls -1 /etc/opendkim/keys/localhost.localdomain/ | wc -l'
   assert_success
   assert_output 2
   # Check keys for otherdomain.tld
   run docker run --rm \
-    -v "$private_config/empty/opendkim":/etc/opendkim \
+    -v "${private_config}/empty/opendkim":/etc/opendkim \
     `docker inspect --format '{{ .Config.Image }}' mail` /bin/sh -c 'ls -1 /etc/opendkim/keys/otherdomain.tld | wc -l'
   assert_success
   assert_output 2
   # Check presence of tables and TrustedHosts
   run docker run --rm \
-    -v "$private_config/empty/opendkim":/etc/opendkim \
+    -v "${private_config}/empty/opendkim":/etc/opendkim \
     `docker inspect --format '{{ .Config.Image }}' mail` /bin/sh -c "ls -1 /etc/opendkim | grep -E 'KeyTable|SigningTable|TrustedHosts|keys'|wc -l"
   assert_success
   assert_output 4
@@ -562,29 +562,29 @@ EOF
 
 @test "checking opendkim: generator creates keys, tables and TrustedHosts without postfix-accounts.cf" {
   private_config="$(duplicate_config_for_container . mail_dkim_generator_creates_keys_tables_TrustedHosts_without_postfix_accounts.cf)"
-  rm -rf "$private_config/without-accounts"
-  mkdir -p "$private_config/without-accounts"
+  rm -rf "${private_config}/without-accounts"
+  mkdir -p "${private_config}/without-accounts"
   run docker run --rm \
-    -v "$private_config/without-accounts/":/tmp/docker-mailserver/ \
-    -v "$private_config/postfix-virtual.cf":/tmp/docker-mailserver/postfix-virtual.cf \
+    -v "${private_config}/without-accounts/":/tmp/docker-mailserver/ \
+    -v "${private_config}/postfix-virtual.cf":/tmp/docker-mailserver/postfix-virtual.cf \
     `docker inspect --format '{{ .Config.Image }}' mail` /bin/sh -c 'generate-dkim-config | wc -l'
   assert_success
   assert_output 5
   # Check keys for localhost.localdomain
   run docker run --rm \
-    -v "$private_config/without-accounts/opendkim":/etc/opendkim \
+    -v "${private_config}/without-accounts/opendkim":/etc/opendkim \
     `docker inspect --format '{{ .Config.Image }}' mail` /bin/sh -c 'ls -1 /etc/opendkim/keys/localhost.localdomain/ | wc -l'
   assert_success
   assert_output 2
   # Check keys for otherdomain.tld
   # run docker run --rm \
-  #   -v "$private_config/without-accounts/opendkim":/etc/opendkim \
+  #   -v "${private_config}/without-accounts/opendkim":/etc/opendkim \
   #   `docker inspect --format '{{ .Config.Image }}' mail` /bin/sh -c 'ls -1 /etc/opendkim/keys/otherdomain.tld | wc -l'
   # assert_success
-  # [ "$output" -eq 0 ]
+  # [ "${output}" -eq 0 ]
   # Check presence of tables and TrustedHosts
   run docker run --rm \
-    -v "$private_config/without-accounts/opendkim":/etc/opendkim \
+    -v "${private_config}/without-accounts/opendkim":/etc/opendkim \
     `docker inspect --format '{{ .Config.Image }}' mail` /bin/sh -c "ls -1 /etc/opendkim | grep -E 'KeyTable|SigningTable|TrustedHosts|keys'|wc -l"
   assert_success
   assert_output 4
@@ -592,29 +592,29 @@ EOF
 
 @test "checking opendkim: generator creates keys, tables and TrustedHosts without postfix-virtual.cf" {
   private_config="$(duplicate_config_for_container . mail_dkim_generator_creates_keys_tables_TrustedHosts_without_postfix_virtual.cf)"
-  rm -rf "$private_config/without-virtual"
-  mkdir -p "$private_config/without-virtual"
+  rm -rf "${private_config}/without-virtual"
+  mkdir -p "${private_config}/without-virtual"
   run docker run --rm \
-    -v "$private_config/without-virtual/":/tmp/docker-mailserver/ \
-    -v "$private_config/postfix-accounts.cf":/tmp/docker-mailserver/postfix-accounts.cf \
+    -v "${private_config}/without-virtual/":/tmp/docker-mailserver/ \
+    -v "${private_config}/postfix-accounts.cf":/tmp/docker-mailserver/postfix-accounts.cf \
     `docker inspect --format '{{ .Config.Image }}' mail` /bin/sh -c 'generate-dkim-config | wc -l'
   assert_success
   assert_output 5
   # Check keys for localhost.localdomain
   run docker run --rm \
-    -v "$private_config/without-virtual/opendkim":/etc/opendkim \
+    -v "${private_config}/without-virtual/opendkim":/etc/opendkim \
     `docker inspect --format '{{ .Config.Image }}' mail` /bin/sh -c 'ls -1 /etc/opendkim/keys/localhost.localdomain/ | wc -l'
   assert_success
   assert_output 2
   # Check keys for otherdomain.tld
   run docker run --rm \
-    -v "$private_config/without-virtual/opendkim":/etc/opendkim \
+    -v "${private_config}/without-virtual/opendkim":/etc/opendkim \
     `docker inspect --format '{{ .Config.Image }}' mail` /bin/sh -c 'ls -1 /etc/opendkim/keys/otherdomain.tld | wc -l'
   assert_success
   assert_output 2
   # Check presence of tables and TrustedHosts
   run docker run --rm \
-    -v "$private_config/without-virtual/opendkim":/etc/opendkim \
+    -v "${private_config}/without-virtual/opendkim":/etc/opendkim \
     `docker inspect --format '{{ .Config.Image }}' mail` /bin/sh -c "ls -1 /etc/opendkim | grep -E 'KeyTable|SigningTable|TrustedHosts|keys'|wc -l"
   assert_success
   assert_output 4
@@ -622,54 +622,54 @@ EOF
 
 @test "checking opendkim: generator creates keys, tables and TrustedHosts using domain name" {
   private_config="$(duplicate_config_for_container . mail_dkim_generator_creates_keys_tables_TrustedHosts_without_postfix_virtual.cf)"
-  rm -rf "$private_config/with-domain" && mkdir -p "$private_config/with-domain"
+  rm -rf "${private_config}/with-domain" && mkdir -p "${private_config}/with-domain"
   run docker run --rm \
-    -v "$private_config/with-domain/":/tmp/docker-mailserver/ \
-    -v "$private_config/postfix-accounts.cf":/tmp/docker-mailserver/postfix-accounts.cf \
-    -v "$private_config/postfix-virtual.cf":/tmp/docker-mailserver/postfix-virtual.cf \
+    -v "${private_config}/with-domain/":/tmp/docker-mailserver/ \
+    -v "${private_config}/postfix-accounts.cf":/tmp/docker-mailserver/postfix-accounts.cf \
+    -v "${private_config}/postfix-virtual.cf":/tmp/docker-mailserver/postfix-virtual.cf \
     `docker inspect --format '{{ .Config.Image }}' mail` /bin/sh -c 'generate-dkim-config | wc -l'
   assert_success
   assert_output 6
   # Generate key using domain name
   run docker run --rm \
-    -v "$private_config/with-domain/":/tmp/docker-mailserver/ \
+    -v "${private_config}/with-domain/":/tmp/docker-mailserver/ \
     `docker inspect --format '{{ .Config.Image }}' mail` /bin/sh -c 'generate-dkim-domain testdomain.tld | wc -l'
   assert_success
   assert_output 1
   # Check keys for localhost.localdomain
   run docker run --rm \
-    -v "$private_config/with-domain/opendkim":/etc/opendkim \
+    -v "${private_config}/with-domain/opendkim":/etc/opendkim \
     `docker inspect --format '{{ .Config.Image }}' mail` /bin/sh -c 'ls -1 /etc/opendkim/keys/localhost.localdomain/ | wc -l'
   assert_success
   assert_output 2
   # Check keys for otherdomain.tld
   run docker run --rm \
-    -v "$private_config/with-domain/opendkim":/etc/opendkim \
+    -v "${private_config}/with-domain/opendkim":/etc/opendkim \
     `docker inspect --format '{{ .Config.Image }}' mail` /bin/sh -c 'ls -1 /etc/opendkim/keys/otherdomain.tld | wc -l'
   assert_success
   assert_output 2
   # Check keys for testdomain.tld
   run docker run --rm \
-    -v "$private_config/with-domain/opendkim":/etc/opendkim \
+    -v "${private_config}/with-domain/opendkim":/etc/opendkim \
     `docker inspect --format '{{ .Config.Image }}' mail` /bin/sh -c 'ls -1 /etc/opendkim/keys/testdomain.tld | wc -l'
   assert_success
   assert_output 2
   # Check presence of tables and TrustedHosts
   run docker run --rm \
-    -v "$private_config/with-domain/opendkim":/etc/opendkim \
+    -v "${private_config}/with-domain/opendkim":/etc/opendkim \
     `docker inspect --format '{{ .Config.Image }}' mail` /bin/sh -c "ls -1 /etc/opendkim | grep -E 'KeyTable|SigningTable|TrustedHosts|keys' | wc -l"
   assert_success
   assert_output 4
   # Check valid entries actually present in KeyTable
   run docker run --rm \
-    -v "$private_config/with-domain/opendkim":/etc/opendkim \
+    -v "${private_config}/with-domain/opendkim":/etc/opendkim \
     `docker inspect --format '{{ .Config.Image }}' mail` /bin/sh -c \
     "egrep 'localhost.localdomain|otherdomain.tld|localdomain2.com|testdomain.tld' /etc/opendkim/KeyTable | wc -l"
   assert_success
   assert_output 4
   # Check valid entries actually present in SigningTable
   run docker run --rm \
-    -v "$private_config/with-domain/opendkim":/etc/opendkim \
+    -v "${private_config}/with-domain/opendkim":/etc/opendkim \
     `docker inspect --format '{{ .Config.Image }}' mail` /bin/sh -c \
     "egrep 'localhost.localdomain|otherdomain.tld|localdomain2.com|testdomain.tld' /etc/opendkim/SigningTable | wc -l"
   assert_success
@@ -731,7 +731,7 @@ EOF
 }
 
 @test "checking amavis: VIRUSMAILS_DELETE_DELAY override works as expected" {
-  run docker run --rm -e VIRUSMAILS_DELETE_DELAY=2 `docker inspect --format '{{ .Config.Image }}' mail` /bin/bash -c 'echo $VIRUSMAILS_DELETE_DELAY | grep 2'
+  run docker run --rm -e VIRUSMAILS_DELETE_DELAY=2 `docker inspect --format '{{ .Config.Image }}' mail` /bin/bash -c 'echo ${VIRUSMAILS_DELETE_DELAY} | grep 2'
   assert_success
 }
 
@@ -867,7 +867,7 @@ EOF
 
   run docker exec mail /bin/sh -c "grep '^user3@domain\.tld|' -i /tmp/docker-mailserver/postfix-accounts.cf"
   assert_success
-  [ ! -z "$output" ]
+  [ ! -z "${output}" ]
 }
 
 @test "checking accounts: auser3 should have been added to /tmp/docker-mailserver/postfix-accounts.cf" {
@@ -875,7 +875,7 @@ EOF
 
   run docker exec mail /bin/sh -c "grep '^auser3@domain\.tld|' -i /tmp/docker-mailserver/postfix-accounts.cf"
   assert_success
-  [ ! -z "$output" ]
+  [ ! -z "${output}" ]
 }
 
 @test "checking accounts: a.ser3 should have been added to /tmp/docker-mailserver/postfix-accounts.cf" {
@@ -883,7 +883,7 @@ EOF
 
   run docker exec mail /bin/sh -c "grep '^a\.ser3@domain\.tld|' -i /tmp/docker-mailserver/postfix-accounts.cf"
   assert_success
-  [ ! -z "$output" ]
+  [ ! -z "${output}" ]
 }
 
 @test "checking accounts: user3 should have been removed from /tmp/docker-mailserver/postfix-accounts.cf but not auser3" {
@@ -891,11 +891,11 @@ EOF
 
   run docker exec mail /bin/sh -c "grep '^user3@domain\.tld' -i /tmp/docker-mailserver/postfix-accounts.cf"
   assert_failure
-  [ -z "$output" ]
+  [ -z "${output}" ]
 
   run docker exec mail /bin/sh -c "grep '^auser3@domain\.tld' -i /tmp/docker-mailserver/postfix-accounts.cf"
   assert_success
-  [ ! -z "$output" ]
+  [ ! -z "${output}" ]
 }
 
 @test "checking user updating password for user in /tmp/docker-mailserver/postfix-accounts.cf" {
@@ -929,20 +929,20 @@ EOF
     -v "$(duplicate_config_for_container without-accounts/ without-accounts-deleting-user)":/tmp/docker-mailserver/ \
     `docker inspect --format '{{ .Config.Image }}' mail` /bin/sh -c 'delmailuser -y user3@domain.tld'
   assert_success
-  [ -z "$output" ]
+  [ -z "${output}" ]
 }
 
 @test "checking accounts: user3 should have been added to /tmp/docker-mailserver/postfix-accounts.cf even when that file does not exist" {
   private_config=$(duplicate_config_for_container without-accounts/ without-accounts_file_does_not_exist)
   run docker run --rm \
-    -v "$private_config/without-accounts/":/tmp/docker-mailserver/ \
+    -v "${private_config}/without-accounts/":/tmp/docker-mailserver/ \
     `docker inspect --format '{{ .Config.Image }}' mail` /bin/sh -c 'addmailuser user3@domain.tld mypassword'
   assert_success
   run docker run --rm \
-    -v "$private_config/without-accounts/":/tmp/docker-mailserver/ \
+    -v "${private_config}/without-accounts/":/tmp/docker-mailserver/ \
     `docker inspect --format '{{ .Config.Image }}' mail` /bin/sh -c 'grep user3@domain.tld -i /tmp/docker-mailserver/postfix-accounts.cf'
   assert_success
-  [ ! -z "$output" ]
+  [ ! -z "${output}" ]
 }
 
 
@@ -1037,35 +1037,35 @@ EOF
 
 @test "checking quota: dovecot mailbox max size must be equal to postfix mailbox max size" {
   postfix_mailbox_size=$(docker exec mail sh -c "postconf | grep -Po '(?<=mailbox_size_limit = )[0-9]+'")
-  run echo "$postfix_mailbox_size"
+  run echo "${postfix_mailbox_size}"
   refute_output ""
 
   # dovecot relies on virtual_mailbox_size by default
   postfix_virtual_mailbox_size=$(docker exec mail sh -c "postconf | grep -Po '(?<=virtual_mailbox_limit = )[0-9]+'")
-  assert_equal "$postfix_virtual_mailbox_size" "$postfix_mailbox_size"
+  assert_equal "${postfix_virtual_mailbox_size}" "${postfix_mailbox_size}"
 
-  postfix_mailbox_size_mb=$(($postfix_mailbox_size / 1000000))
+  postfix_mailbox_size_mb=$(( postfix_mailbox_size / 1000000))
 
   dovecot_mailbox_size_mb=$(docker exec mail sh -c "doveconf | grep  -oP '(?<=quota_rule \= \*\:storage=)[0-9]+'")
-  run echo "$dovecot_mailbox_size_mb"
+  run echo "${dovecot_mailbox_size_mb}"
   refute_output ""
 
-  assert_equal "$postfix_mailbox_size_mb" "$dovecot_mailbox_size_mb"
+  assert_equal "${postfix_mailbox_size_mb}" "${dovecot_mailbox_size_mb}"
 }
 
 
 @test "checking quota: dovecot message max size must be equal to postfix messsage max size" {
   postfix_message_size=$(docker exec mail sh -c "postconf | grep -Po '(?<=message_size_limit = )[0-9]+'")
-  run echo "$postfix_message_size"
+  run echo "${postfix_message_size}"
   refute_output ""
 
-  postfix_message_size_mb=$(($postfix_message_size / 1000000))
+  postfix_message_size_mb=$((${postfix_message_size} / 1000000))
 
   dovecot_message_size_mb=$(docker exec mail sh -c "doveconf | grep  -oP '(?<=quota_max_mail_size = )[0-9]+'")
-  run echo "$dovecot_message_size_mb"
+  run echo "${dovecot_message_size_mb}"
   refute_output ""
 
-  assert_equal "$postfix_message_size_mb" "$dovecot_message_size_mb"
+  assert_equal "${postfix_message_size_mb}" "${dovecot_message_size_mb}"
 }
 
 @test "checking quota: quota directive is removed when mailbox is removed" {
@@ -1207,7 +1207,7 @@ EOF
   assert_success
 
   value=$(cat $(private_config_path mail)/postfix-accounts.cf | grep setup_email_add@example.com | awk -F '|' '{print $1}')
-  [ "$value" = "setup_email_add@example.com" ]
+  [ "${value}" = "setup_email_add@example.com" ]
   assert_success
 
   wait_for_changes_to_be_detected_in_container mail
@@ -1233,20 +1233,20 @@ EOF
   assert_success
 
   initialpass=$(cat $(private_config_path mail)/postfix-accounts.cf | grep lorem@impsum.org | awk -F '|' '{print $2}')
-  [ "$initialpass" != "" ]
+  [ "${initialpass}" != "" ]
   assert_success
 
   run ./setup.sh -c mail email update lorem@impsum.org my password
   assert_success
 
   updatepass=$(cat $(private_config_path mail)/postfix-accounts.cf | grep lorem@impsum.org | awk -F '|' '{print $2}')
-  [ "$updatepass" != "" ]
+  [ "${updatepass}" != "" ]
   assert_success
 
-  [ "$initialpass" != "$updatepass" ]
+  [ "${initialpass}" != "${updatepass}" ]
   assert_success
 
-  docker exec mail doveadm pw -t "$updatepass" -p 'my password' | grep 'verified'
+  docker exec mail doveadm pw -t "${updatepass}" -p 'my password' | grep 'verified'
   assert_success
 }
 
@@ -1395,8 +1395,8 @@ EOF
 # debug
 @test "checking setup.sh: setup.sh debug fetchmail" {
   run ./setup.sh -c mail debug fetchmail
-  [ "$status" -eq 11 ]
-  [[ "$output" == *"fetchmail: normal termination, status 11"* ]]
+  [ "${status}" -eq 11 ]
+  [[ "${output}" == *"fetchmail: normal termination, status 11"* ]]
 }
 @test "checking setup.sh: setup.sh debug inspect" {
   run ./setup.sh -c mail debug inspect