diff --git a/test/Dockerfile-alpine b/test/Dockerfile-alpine
index 924950b..2c28f48 100644
--- a/test/Dockerfile-alpine
+++ b/test/Dockerfile-alpine
@@ -8,8 +8,7 @@ WORKDIR /root
 
 # Create nginx directories in standard places
 RUN mkdir /run/nginx
-RUN mkdir /etc/nginx/pki
-RUN mkdir /etc/nginx/pki/private
+RUN mkdir -p /etc/nginx/pki/private
 
 # Setup ftp
 ENV VSFTPD_CONF=/etc/vsftpd.conf
@@ -24,11 +23,11 @@ RUN chown -R ftpuser.www-data /var/www
 RUN chmod g+w -R /var/www
 
 # 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 git clone --depth 1 https://github.com/bats-core/bats-core.git /bats-core --branch v1.2.1
+RUN git clone --depth 1 https://github.com/bats-core/bats-support /bats-support
+RUN git clone --depth 1 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
+CMD [ "tail", "-f", "/dev/null" ]
diff --git a/test/Dockerfile-centos6 b/test/Dockerfile-centos6
index a8d59b0..e16388f 100644
--- a/test/Dockerfile-centos6
+++ b/test/Dockerfile-centos6
@@ -30,8 +30,7 @@ RUN chown -R www-data.www-data /var/www
 RUN chmod g+w -R /var/www
 
 WORKDIR /root
-RUN mkdir /etc/nginx/pki
-RUN mkdir /etc/nginx/pki/private
+RUN mkdir -p /etc/nginx/pki/private
 COPY ./test/test-config/nginx-ubuntu-no-ssl /etc/nginx/conf.d/default.conf
 
 # BATS (Bash Automated Testings)
@@ -45,4 +44,4 @@ ENV CI=yes
 EXPOSE 80 443
 
 # Run eternal loop - for testing
-CMD tail -f /dev/null
+CMD [ "tail", "-f", "/dev/null" ]
diff --git a/test/Dockerfile-centos7 b/test/Dockerfile-centos7
index 8bf8fa9..794e0bd 100644
--- a/test/Dockerfile-centos7
+++ b/test/Dockerfile-centos7
@@ -8,8 +8,7 @@ RUN yum -y install ftp vsftpd
 RUN yum -y install openssh-server
 
 WORKDIR /root
-RUN mkdir /etc/nginx/pki
-RUN mkdir /etc/nginx/pki/private
+RUN mkdir -p /etc/nginx/pki/private
 COPY ./test/test-config/nginx-ubuntu-no-ssl /etc/nginx/conf.d/default.conf
 COPY ./test/test-config/nginx-centos7.conf /etc/nginx/nginx.conf
 
@@ -27,7 +26,7 @@ RUN chown -R www-data.www-data /var/www
 RUN chmod g+w -R /var/www
 
 # 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 git clone --depth 1 https://github.com/bats-core/bats-core.git /bats-core --branch v1.2.1
+RUN git clone --depth 1 https://github.com/bats-core/bats-support /bats-support
+RUN git clone --depth 1 https://github.com/bats-core/bats-assert /bats-assert
 RUN /bats-core/install.sh /usr/local
diff --git a/test/Dockerfile-centos7-duckdns b/test/Dockerfile-centos7-duckdns
index 719c9de..bf85592 100644
--- a/test/Dockerfile-centos7-duckdns
+++ b/test/Dockerfile-centos7-duckdns
@@ -12,18 +12,17 @@ ENV dynamic_dns "dynu"
 ENV DUCKDNS_TOKEN 1d616aa9-b8e4-4bb4-b312-3289de82badb
 
 WORKDIR /root
-RUN mkdir /etc/nginx/pki
-RUN mkdir /etc/nginx/pki/private
+RUN mkdir -p /etc/nginx/pki/private
 COPY ./test/test-config/nginx-ubuntu-no-ssl /etc/nginx/conf.d/default.conf
 COPY ./test/test-config/nginx-centos7.conf /etc/nginx/nginx.conf
 
 # 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 git clone --depth 1 https://github.com/bats-core/bats-core.git /bats-core --branch v1.2.1
+RUN git clone --depth 1 https://github.com/bats-core/bats-support /bats-support
+RUN git clone --depth 1 https://github.com/bats-core/bats-assert /bats-assert
 RUN /bats-core/install.sh /usr/local
 
 EXPOSE 80 443
 
 # Run eternal loop - for testing
-CMD tail -f /dev/null
+CMD [ "tail", "-f", "/dev/null" ]
diff --git a/test/Dockerfile-centos8 b/test/Dockerfile-centos8
index 64f4381..210bd8e 100644
--- a/test/Dockerfile-centos8
+++ b/test/Dockerfile-centos8
@@ -10,8 +10,7 @@ RUN yum -y install ftp vsftpd
 RUN yum -y install openssh-server
 
 WORKDIR /root
-RUN mkdir /etc/nginx/pki
-RUN mkdir /etc/nginx/pki/private
+RUN mkdir -p /etc/nginx/pki/private
 COPY ./test/test-config/nginx-ubuntu-no-ssl /etc/nginx/conf.d/default.conf
 COPY ./test/test-config/nginx-centos7.conf /etc/nginx/nginx.conf
 
@@ -29,7 +28,7 @@ RUN chown -R www-data.www-data /var/www
 RUN chmod g+w -R /var/www
 
 # 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 git clone --depth 1 https://github.com/bats-core/bats-core.git /bats-core --branch v1.2.1
+RUN git clone --depth 1 https://github.com/bats-core/bats-support /bats-support
+RUN git clone --depth 1 https://github.com/bats-core/bats-assert /bats-assert
 RUN /bats-core/install.sh /usr/local
diff --git a/test/Dockerfile-debian b/test/Dockerfile-debian
index fa74995..04e5232 100644
--- a/test/Dockerfile-debian
+++ b/test/Dockerfile-debian
@@ -9,8 +9,7 @@ RUN apt-get install -y ftp vsftpd
 RUN apt-get install -y openssh-server
 
 WORKDIR /root
-RUN mkdir /etc/nginx/pki
-RUN mkdir /etc/nginx/pki/private
+RUN mkdir -p /etc/nginx/pki/private
 
 # Setup ftp
 ENV VSFTPD_CONF=/etc/vsftpd.conf
@@ -24,10 +23,10 @@ RUN chown -R www-data.www-data /var/www
 RUN chmod g+w -R /var/www
 
 # 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 git clone --depth 1 https://github.com/bats-core/bats-core.git /bats-core --branch v1.2.1
+RUN git clone --depth 1 https://github.com/bats-core/bats-support /bats-support
+RUN git clone --depth 1 https://github.com/bats-core/bats-assert /bats-assert
 RUN /bats-core/install.sh /usr/local
 
 # Run eternal loop - for testing
-CMD tail -f /dev/null
+CMD [ "tail", "-f", "/dev/null" ]
diff --git a/test/Dockerfile-ubuntu b/test/Dockerfile-ubuntu
index 68813f8..dd8338d 100644
--- a/test/Dockerfile-ubuntu
+++ b/test/Dockerfile-ubuntu
@@ -29,10 +29,10 @@ WORKDIR /root
 RUN touch /root/.rnd
 
 # 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 git clone --depth 1 https://github.com/bats-core/bats-core.git /bats-core --branch v1.2.1
+RUN git clone --depth 1 https://github.com/bats-core/bats-support /bats-support
+RUN git clone --depth 1 https://github.com/bats-core/bats-assert /bats-assert
 RUN /bats-core/install.sh /usr/local
 
 # Run eternal loop - for testing
-CMD tail -f /dev/null
+CMD [ "tail", "-f", "/dev/null" ]
diff --git a/test/Dockerfile-ubuntu-duckdns b/test/Dockerfile-ubuntu-duckdns
index f4cf9e3..a07bb23 100644
--- a/test/Dockerfile-ubuntu-duckdns
+++ b/test/Dockerfile-ubuntu-duckdns
@@ -21,10 +21,10 @@ WORKDIR /root
 RUN touch /root/.rnd
 
 # 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 git clone --depth 1 https://github.com/bats-core/bats-core.git /bats-core --branch v1.2.1
+RUN git clone --depth 1 https://github.com/bats-core/bats-support /bats-support
+RUN git clone --depth 1 https://github.com/bats-core/bats-assert /bats-assert
 RUN /bats-core/install.sh /usr/local
 
 # Run eternal loop - for testing
-CMD tail -f /dev/null
+CMD [ "tail", "-f", "/dev/null" ]
diff --git a/test/Dockerfile-ubuntu16 b/test/Dockerfile-ubuntu16
index 184db87..00a4589 100644
--- a/test/Dockerfile-ubuntu16
+++ b/test/Dockerfile-ubuntu16
@@ -10,8 +10,7 @@ RUN apt-get install -y ftp vsftpd
 RUN apt-get install -y openssh-server
 
 WORKDIR /root
-RUN mkdir /etc/nginx/pki
-RUN mkdir /etc/nginx/pki/private
+RUN mkdir -p /etc/nginx/pki/private
 COPY ./test/test-config/nginx-ubuntu-no-ssl /etc/nginx/sites-enabled/default
 
 # Setup ftp
@@ -28,10 +27,10 @@ RUN chown -R www-data.www-data /var/www
 RUN chmod g+w -R /var/www
 
 # 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 git clone --depth 1 https://github.com/bats-core/bats-core.git /bats-core --branch v1.2.1
+RUN git clone --depth 1 https://github.com/bats-core/bats-support /bats-support
+RUN git clone --depth 1 https://github.com/bats-core/bats-assert /bats-assert
 RUN /bats-core/install.sh /usr/local
 
 # Run eternal loop - for testing
-CMD tail -f /dev/null
+CMD [ "tail", "-f", "/dev/null" ]
diff --git a/test/Dockerfile-ubuntu18 b/test/Dockerfile-ubuntu18
index ed1fae3..91a0429 100644
--- a/test/Dockerfile-ubuntu18
+++ b/test/Dockerfile-ubuntu18
@@ -10,8 +10,7 @@ RUN apt-get install -y ftp vsftpd
 RUN apt-get install -y openssh-server
 
 WORKDIR /root
-RUN mkdir /etc/nginx/pki
-RUN mkdir /etc/nginx/pki/private
+RUN mkdir -p /etc/nginx/pki/private
 COPY ./test/test-config/nginx-ubuntu-no-ssl /etc/nginx/sites-enabled/default
 
 # Setup ftp
@@ -31,12 +30,12 @@ RUN chmod g+w -R /var/www
 RUN touch /root/.rnd
 
 # 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 git clone --depth 1 https://github.com/bats-core/bats-core.git /bats-core --branch v1.2.1
+RUN git clone --depth 1 https://github.com/bats-core/bats-support /bats-support
+RUN git clone --depth 1 https://github.com/bats-core/bats-assert /bats-assert
 RUN /bats-core/install.sh /usr/local
 
 EXPOSE 80 443
 
 # Run eternal loop - for testing
-CMD tail -f /dev/null
+CMD [ "tail", "-f", "/dev/null" ]