diff --git a/.github/workflows/run-tests-pebble.yml b/.github/workflows/run-tests-pebble.yml
index 0e26962b..5dc53a4c 100644
--- a/.github/workflows/run-tests-pebble.yml
+++ b/.github/workflows/run-tests-pebble.yml
@@ -15,6 +15,38 @@ jobs:
         run: docker-compose up -d --build
       - name: Run test suite on Alpine
         run: test/run-test.sh alpine
+  test-bash-4-0:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v1
+      - name: Build the docker-compose stack
+        run: docker-compose up -d --build
+      - name: Run test suite on Alpine using Bash 4.0
+        run: test/run-test.sh bash4-0
+  test-bash-4-2:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v1
+      - name: Build the docker-compose stack
+        run: docker-compose up -d --build
+      - name: Run test suite on Alpine using Bash 4.2
+        run: test/run-test.sh bash4-2
+  test-bash-5-0:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v1
+      - name: Build the docker-compose stack
+        run: docker-compose up -d --build
+      - name: Run test suite on Alpine using Bash 5
+        run: test/run-test.sh bash5-0
+  test-centos6:
+      runs-on: ubuntu-latest
+      steps:
+        - uses: actions/checkout@v1
+        - name: Build the docker-compose stack
+          run: docker-compose up -d --build
+        - name: Run test suite on CentOS6
+          run: test/run-test.sh centos6
   test-centos7:
       runs-on: ubuntu-latest
       steps:
diff --git a/test/Dockerfile-bash4-0 b/test/Dockerfile-bash4-0
new file mode 100644
index 00000000..e75b74aa
--- /dev/null
+++ b/test/Dockerfile-bash4-0
@@ -0,0 +1,22 @@
+FROM bash:4.0
+
+# https://hub.docker.com/_/bash
+
+RUN apk --no-cache add supervisor openssl git curl bind-tools drill wget nginx bash
+
+WORKDIR /root
+
+# Create nginx directories in standard places
+RUN mkdir /run/nginx
+RUN mkdir /etc/nginx/pki
+RUN mkdir /etc/nginx/pki/private
+
+# BATS (Bash Automated Testings)
+RUN git clone https://github.com/bats-core/bats-core.git /bats-core --branch v1.2.1
+RUN git clone https://github.com/bats-core/bats-support /bats-support
+RUN git clone https://github.com/bats-core/bats-assert /bats-assert
+RUN /bats-core/install.sh /usr/local
+
+# Use supervisord to run nginx in the background
+COPY ./test/test-config/alpine-supervisord.conf /etc/supervisord.conf
+CMD tail -f /dev/null
diff --git a/test/Dockerfile-bash4-2 b/test/Dockerfile-bash4-2
new file mode 100644
index 00000000..720884cb
--- /dev/null
+++ b/test/Dockerfile-bash4-2
@@ -0,0 +1,22 @@
+FROM bash:4.2
+
+# https://hub.docker.com/_/bash
+
+RUN apk --no-cache add supervisor openssl git curl bind-tools drill wget nginx bash
+
+WORKDIR /root
+
+# Create nginx directories in standard places
+RUN mkdir /run/nginx
+RUN mkdir /etc/nginx/pki
+RUN mkdir /etc/nginx/pki/private
+
+# BATS (Bash Automated Testings)
+RUN git clone https://github.com/bats-core/bats-core.git /bats-core --branch v1.2.1
+RUN git clone https://github.com/bats-core/bats-support /bats-support
+RUN git clone https://github.com/bats-core/bats-assert /bats-assert
+RUN /bats-core/install.sh /usr/local
+
+# Use supervisord to run nginx in the background
+COPY ./test/test-config/alpine-supervisord.conf /etc/supervisord.conf
+CMD tail -f /dev/null
diff --git a/test/Dockerfile-bash5-0 b/test/Dockerfile-bash5-0
new file mode 100644
index 00000000..ba0295a0
--- /dev/null
+++ b/test/Dockerfile-bash5-0
@@ -0,0 +1,22 @@
+FROM bash:5.0
+
+# https://hub.docker.com/_/bash
+
+RUN apk --no-cache add supervisor openssl git curl bind-tools drill wget nginx bash
+
+WORKDIR /root
+
+# Create nginx directories in standard places
+RUN mkdir /run/nginx
+RUN mkdir /etc/nginx/pki
+RUN mkdir /etc/nginx/pki/private
+
+# BATS (Bash Automated Testings)
+RUN git clone https://github.com/bats-core/bats-core.git /bats-core --branch v1.2.1
+RUN git clone https://github.com/bats-core/bats-support /bats-support
+RUN git clone https://github.com/bats-core/bats-assert /bats-assert
+RUN /bats-core/install.sh /usr/local
+
+# Use supervisord to run nginx in the background
+COPY ./test/test-config/alpine-supervisord.conf /etc/supervisord.conf
+CMD tail -f /dev/null
diff --git a/test/Dockerfile-centos6 b/test/Dockerfile-centos6
index d578f4b1..6874cb27 100644
--- a/test/Dockerfile-centos6
+++ b/test/Dockerfile-centos6
@@ -5,8 +5,14 @@ FROM centos:centos6
 # [wsl2]
 # kernelCommandLine = vsyscall=emulate
 
+# Centos 6 is EOL and is no longer available from the usual mirrors, so switch
+# to https://vault.centos.org
+RUN sed -i 's/enabled=1/enabled=0/g' /etc/yum/pluginconf.d/fastestmirror.conf && \
+    sed -i 's/^mirrorlist/#mirrorlist/g' /etc/yum.repos.d/*.repo && \
+    sed -i 's;^#baseurl=http://mirror;baseurl=https://vault;g' /etc/yum.repos.d/*.repo
+
 # Update and install required software
-RUN yum -y update
+#RUN yum -y update
 RUN yum -y install epel-release
 RUN yum -y install git curl dnsutils ldns wget nginx
 
diff --git a/test/run-test.cmd b/test/run-test.cmd
index ed6ad6ea..d33c0053 100644
--- a/test/run-test.cmd
+++ b/test/run-test.cmd
@@ -10,6 +10,7 @@ set COMMAND=%2 %3
 REM check if OS *contains* staging
 IF NOT x%OS:duck=%==x%OS% GOTO duckdns
 IF NOT x%OS:dynu=%==x%OS% GOTO dynu
+IF NOT x%OS:bash=%==x%OS% GOTO bash
 set ALIAS=%OS%.getssl.test
 set STAGING=
 set GETSSL_OS=%OS%
@@ -34,6 +35,12 @@ GOTO Run
 set ALIAS=%OS:-dynu=%-getssl.freeddns.org
 set STAGING=--env STAGING=true --env dynamic_dns=dynu
 set GETSSL_OS=%OS:-dynu=%
+GOTO Run
+
+:bash
+set ALIAS=%OS%.getssl.test
+set STAGING=
+set GETSSL_OS=alpine
 
 :Run
 for %%I in (.) do set CurrDirName=%%~nxI
diff --git a/test/run-test.sh b/test/run-test.sh
index 18443cd2..ef7e403f 100755
--- a/test/run-test.sh
+++ b/test/run-test.sh
@@ -1,31 +1,33 @@
 #! /usr/bin/env bash
 
 if [ $# -eq 0 ]; then
-    echo "Usage: $(basename "$0") <os> [<command>]"
-    echo "e.g. $(basename "$0") alpine bats /getssl/test"
-    exit 1
+  echo "Usage: $(basename "$0") <os> [<command>]"
+  echo "e.g. $(basename "$0") alpine bats /getssl/test"
+  exit 1
 fi
 OS=$1
 
 if [ $# -gt 1 ]; then
-    shift
-    COMMAND=$*
+  shift
+  COMMAND=$*
 else
-    COMMAND="bats /getssl/test --timing"
+  COMMAND="bats /getssl/test --timing"
 fi
 
+ALIAS="$OS.getssl.test"
+STAGING=""
+GETSSL_OS=$OS
+
 if [[ "$OS" == *"duckdns"* ]]; then
-    ALIAS="${OS%-duckdns}-getssl.duckdns.org"
-    STAGING="--env STAGING=true --env dynamic_dns=duckdns"
-    GETSSL_OS="${OS%-duckdns}"
+  ALIAS="${OS%-duckdns}-getssl.duckdns.org"
+  STAGING="--env STAGING=true --env dynamic_dns=duckdns"
+  GETSSL_OS="${OS%-duckdns}"
 elif [[ "$OS" == *"dynu"* ]]; then
-    ALIAS="${OS%-dynu}-getssl.freeddns.org"
-    STAGING="--env STAGING=true --env dynamic_dns=dynu"
-    GETSSL_OS="${OS%-dynu}"
-else
-    ALIAS="$OS.getssl.test"
-    STAGING=""
-    GETSSL_OS=$OS
+  ALIAS="${OS%-dynu}-getssl.freeddns.org"
+  STAGING="--env STAGING=true --env dynamic_dns=dynu"
+  GETSSL_OS="${OS%-dynu}"
+elif [[ "$OS" == "bash"* ]]; then
+  GETSSL_OS="alpine"
 fi
 
 docker build --rm -f "test/Dockerfile-$OS" -t "getssl-$OS" .