diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 9f86836a..c7117fc7 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -46,15 +46,10 @@ stages:
     - ls
     - docker info
 
-.template_ubuntu_1510: &ubuntu_1510
+.template_ubuntu: &ubuntu
   <<: *ubuntu
   variables:
-    UBUNTU_VERSION: "15.10"
-
-.template_ubuntu_1604: &ubuntu_1604
-  <<: *ubuntu
-  variables:
-    UBUNTU_VERSION: "16.04"
+    UBUNTU_VERSION: "18.04"
 
 ############################################
 # Build stage
@@ -98,18 +93,14 @@ build_netgen_win64:
 .template_build_linux: &build_linux
   stage: build
   script:
-    - docker build -t netgen_${CI_BUILD_REF_NAME}:${UBUNTU_VERSION} -f tests/docker_${UBUNTU_VERSION} .
+    - docker build -t netgen_${CI_BUILD_REF_NAME}:${UBUNTU_VERSION} -f tests/dockerfile .
     - rm -f netgen_${CI_BUILD_REF_NAME}_$UBUNTU_VERSION.id
     - docker run --cidfile netgen_${CI_BUILD_REF_NAME}_${UBUNTU_VERSION}.id -e CCACHE_DIR=/ccache -v /mnt/ccache:/ccache netgen_${CI_BUILD_REF_NAME}:${UBUNTU_VERSION} bash /root/src/netgen/tests/build.sh
     - docker commit `cat netgen_${CI_BUILD_REF_NAME}_${UBUNTU_VERSION}.id` netgen_${CI_BUILD_REF_NAME}_installed:${UBUNTU_VERSION}
     - rm netgen_${CI_BUILD_REF_NAME}_${UBUNTU_VERSION}.id
 
-.build_ubuntu_1510:
-  <<: *ubuntu_1510
-  <<: *build_linux
-
-build_ubuntu_1604:
-  <<: *ubuntu_1604
+build_ubuntu:
+  <<: *ubuntu
   <<: *build_linux
 
 
@@ -145,11 +136,8 @@ test_win64:
       netgen_${CI_BUILD_REF_NAME}_installed:${UBUNTU_VERSION}
       bash -c 'cd /root/build/netgen && make test_netgen ARGS="-V"'
 
-.test_ubuntu_1510:
-  <<: *ubuntu_1510
-  <<: *test_linux
-test_ubuntu_1604:
-  <<: *ubuntu_1604
+test_ubuntu:
+  <<: *ubuntu
   <<: *test_linux
 
 ############################################
diff --git a/tests/build.sh b/tests/build.sh
index 68aea3ad..d2727b2c 100755
--- a/tests/build.sh
+++ b/tests/build.sh
@@ -1,6 +1,6 @@
 cd
 mkdir -p build/netgen
 cd build/netgen
-cmake ../../src/netgen -DUSE_CCACHE=ON
+cmake ../../src/netgen -DUSE_CCACHE=ON -DENABLE_CPP_CORE_GUIDELINES_CHECK=ON
 make -j12
 make install
diff --git a/tests/docker_16.04 b/tests/docker_16.04
deleted file mode 100644
index 2195714b..00000000
--- a/tests/docker_16.04
+++ /dev/null
@@ -1,4 +0,0 @@
-FROM ubuntu:16.04
-MAINTAINER Matthias Hochsteger <matthias.hochsteger@tuwien.ac.at>
-RUN apt-get update && apt-get -y install python3 libpython3-dev libxmu-dev tk-dev tcl-dev cmake git g++ libglu1-mesa-dev ccache python3-pytest python3-numpy python3-tk
-ADD . /root/src/netgen
diff --git a/tests/docker_15.10 b/tests/dockerfile
similarity index 75%
rename from tests/docker_15.10
rename to tests/dockerfile
index b386f250..b215db7a 100644
--- a/tests/docker_15.10
+++ b/tests/dockerfile
@@ -1,4 +1,4 @@
-FROM ubuntu:15.10
+FROM ubuntu:18.04
 MAINTAINER Matthias Hochsteger <matthias.hochsteger@tuwien.ac.at>
-RUN apt-get update && apt-get -y install python3 libpython3-dev libxmu-dev tk-dev tcl-dev cmake git g++ libglu1-mesa-dev ccache python3-pytest python3-numpy python3-tk
+RUN apt-get update && apt-get -y install python3 libpython3-dev libxmu-dev tk-dev tcl-dev cmake git g++ libglu1-mesa-dev ccache python3-pytest python3-numpy python3-tk clang-tidy
 ADD . /root/src/netgen