Last week, Jason Turner presented an intro to Travis CI. I’ve never used it but have wanted to try for a while, so I gave it a shot. Here is a short summary of this small adventure…

First of all, what are these tools we are talking about?

• Travis CI: a build farm for GNU/Linux and Mac OS X that also runs your unit tests
• Coveralls: it works on the top of Travis CI, by generating coverage report (lcov on Linux)
• Appveyor: like Travis CI, but for Windows

TL;DR

You can checkout all the configuration files on this github demo project

To start, simply sign in with your GitHub account on Travis CI, this will import all your repositories. From there, just enable one of them and add the following .travis.yml to your repo:

dist: trusty
sudo: false
language: cpp
  
script:
  - cmake .
  - cmake --build .

On git push, it will automatically trigger your first Travis build.

GCC 6 & Clang 5

By default, Travis CI is using a quite old version of GCC — 4.8, so no C++14 support. Switching to GCC 5 is quite simple and Jason explains in his video how to change the .travis.yml. The one for GCC 6 is almost identical:

dist: trusty
sudo: false
language: cpp

addons:
  apt:
    sources:
      - ubuntu-toolchain-r-test
    packages:
      - g++-6 

script:
  - CXX=/usr/bin/g++-6 CC=/usr/bin/gcc-6 cmake .
  - cmake --build .

Here, we are using the apt add-on to install the g++-6 package. You can add any packages or libraries on which your project depends. Alternatively, you can also use the last clang release to build your project:

dist: trusty
sudo: false
language: cpp

addons:
  apt:
    sources:
      - llvm-toolchain-trusty-5.0
    packages:
      - clang-5.0

script:
  - CXX=/usr/bin/clang++-5.0 CC=/usr/bin/clang-5.0 cmake .
  - cmake --build .

Google Test

GTest is not handled by default — and we cannot blame Travis for that, but more Ubuntu that decided to stop distributing the library package. This means that your CMake FindPackage will fail:

CMake Error at /usr/share/cmake-3.2/Modules/FindPackageHandleStandardArgs.cmake:138 (message):
  Could NOT find GTest (missing: GTEST_LIBRARY GTEST_MAIN_LIBRARY)
Call Stack (most recent call first):
  /usr/share/cmake-3.2/Modules/FindPackageHandleStandardArgs.cmake:374 (_FPHSA_FAILURE_MESSAGE)
  /usr/share/cmake-3.2/Modules/FindGTest.cmake:204 (FIND_PACKAGE_HANDLE_STANDARD_ARGS)

  CMakeLists.txt:21 (find_package)
-- Configuring incomplete, errors occurred!

I looked around and found that people solve this in various ways:

1. With a pre-build bash script that installs the libgtest-dev package, builds it and copies the libraries — this is quite hacky and fragile as it depends on the various system paths and library names.
2. With the GTest source in the repo — importing the whole source tree isn’t necessary
3. By adding GTest as a submodule — this is the way to go

Add GTest as a submodule: git submodule add git@github.com:google/googletest.git gtest

Then create a gtest.cmake file with this content:

set(GOOGLETEST_ROOT gtest/googletest CACHE STRING "Google Test source root")

include_directories(SYSTEM
    ${PROJECT_SOURCE_DIR}/${GOOGLETEST_ROOT}
    ${PROJECT_SOURCE_DIR}/${GOOGLETEST_ROOT}/include
    )

set(GOOGLETEST_SOURCES
    ${PROJECT_SOURCE_DIR}/${GOOGLETEST_ROOT}/src/gtest-all.cc
    ${PROJECT_SOURCE_DIR}/${GOOGLETEST_ROOT}/src/gtest_main.cc
    )

foreach(_source ${GOOGLETEST_SOURCES})
    set_source_files_properties(${_source} PROPERTIES GENERATED 1)
endforeach()

add_library(gtest ${GOOGLETEST_SOURCES})

Note the SYSTEM keyword in include_directories. Without it, you will get spammed on every build by all the warnings from GTest, especially if you build with -Wall -Wextra etc.

Last step, include it in your main CMakeLists.txt and link to gtest:

cmake_minimum_required(VERSION ...)

project(...)
include(gtest.cmake)
...

# GTest needs threading support
find_package (Threads)
target_link_libraries(... gtest ${CMAKE_THREAD_LIBS_INIT})

Coveralls

As you did for Travis CI, you need to sign in with your GitHub account on Coveralls and enable your project.

Now edit your .travis.yml to install and run cpp-coveralls:

dist: trusty
sudo: false
language: cpp

addons:
  apt:
    sources:
      - ubuntu-toolchain-r-test
    packages:
      - g++-6

before_install:
  - pip install --user cpp-coveralls

script:
  - CXX=/usr/bin/g++-6 CC=/usr/bin/gcc-6 cmake -DCOVERAGE=1 .
  - cmake --build . 
  - ./tests

after_success:
  - coveralls --root . -E ".*gtest.*" -E ".*CMakeFiles.*"

A few things to note here:

1. We excluded Google Test from the coverage with -E “.*gtest.*”
2. -DCOVERAGE=1 is passed to CMake — locally, you might not want to enable coverage
3. Don’t forget to run your unit tests if you want them in the coverage report

Finally, we need to enable the gcda files generation — needed by lcov — in our toolchain. This is done by adding the –coverage flag to both compiler and linker:

SET(COVERAGE OFF CACHE BOOL "Coverage")
...
if (COVERAGE)
    target_compile_options(tests PRIVATE --coverage)
    target_link_libraries(tests PRIVATE --coverage)
endif()

Appveyor

As a Linux user, Appveyor was a bit tricky as I couldn’t build locally. Be sure to remember:

• Appveyor will NOT clone your project with git clone –recursive, so you need to run manually git submodule update –init –recursive after the checkout
• It is not possible to build directly with CMake — Appveyor expects a sln file, you can generate it via CMake, e.g. cmake -G “Visual Studio 15 2017 Win64”
• The last 1.8.0 release of GTest does not build with Visual Studio 2017 — you need to add the definition GTEST_HAS_TR1_TUPLE=0 to tell GTest not using ::tr1 stuff

Here is my appveyor.yml file:

version: '1.0.{build}'

image: Visual Studio 2017

platform:
  - x64
 
configuration:
  - Release
  - Debug

install:
    - git submodule update --init --recursive

before_build:
    - cmake -G "Visual Studio 15 2017 Win64" .

build:
  project: $(APPVEYOR_BUILD_FOLDER)\$(APPVEYOR_PROJECT_NAME).sln

test_script:
  - '%APPVEYOR_BUILD_FOLDER%\%CONFIGURATION%\tests.exe'