Add basic test application that runs under CI

.github/workflows/build.yml

@@ -18,7 +18,7 @@ jobs:
       - name: Build
         run: |
           cmake .
-          make
+          make -j2
 
       - name: Package
         run: |
@@ -36,14 +36,24 @@ jobs:
       - uses: actions/checkout@v2
       - name: Install deps
         run: |
-          sudo apt-get install g++ cmake libxxf86vm-dev libgles2-mesa-dev libpng-dev libjpeg-dev zlib1g-dev -qyy
+          sudo apt-get install g++ cmake libxxf86vm-dev libgles2-mesa-dev libpng-dev libjpeg-dev zlib1g-dev xvfb -qyy
 
       - name: Build
         run: |
           sed '/#define _IRR_COMPILE_WITH_OGLES2_/ s|^//||g' -i include/IrrCompileConfig.h
           sed '/#define _IRR_COMPILE_WITH_OPENGL_/ s|^|//|g' -i include/IrrCompileConfig.h
-          cmake .
-          make
+          cmake . -DBUILD_EXAMPLES=1
+          make -j2
+
+      - name: Test (headless)
+        run: |
+          cd bin/Linux
+          ./AutomatedTest null
+
+      - name: Test (Xvfb)
+        run: |
+          cd bin/Linux
+          LIBGL_ALWAYS_SOFTWARE=true xvfb-run ./AutomatedTest
 
   win32:
     runs-on: ubuntu-18.04