Add tests to CI

.gitlab-ci.yml

 image: rikorose/gcc-cmake
 
+stages:
+  - build
+  - test
+
 before_script:
   - g++ --version
 
 build:
+  stage: build
   script:
     - cmake . -DCMAKE_CXX_FLAGS="-Werror"
     - make -j4
@@ -11,7 +16,15 @@ build:
     - cmake . -DCMAKE_CXX_FLAGS="-Wall -Wextra" # Build again, but with more warnings
     - make -j4
 
+tests:
+  stage: test
+  script:
+    - cmake .
+    - make tests -j4
+    - ./tests
+
 cppcheck:
+  stage: build
   before_script:
     - apt-get update -qq && apt-get install -y -qq cppcheck
     - cppcheck --version
@@ -19,6 +32,7 @@ cppcheck:
     - bash -x ci/cppcheck.sh
 
 vera:
+  stage: build
   before_script:
     - apt-get update -qq && apt-get install -y -qq vera++
     - vera++ --version
@@ -27,6 +41,7 @@ vera:
     - bash -x ci/vera.sh
 
 clang-tidy:
+  stage: build
   before_script:
     - apt-get update -qq && apt-get install -y -qq clang-tidy-4.0
     - clang-tidy-4.0 --version