gl2ps: add test

Closes Homebrew/homebrew#36924.

Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>

Formula/gl2ps.rb

@@ -1,5 +1,3 @@
-require "formula"
-
 class Gl2ps < Formula
   homepage "http://www.geuz.org/gl2ps/"
   url "http://geuz.org/gl2ps/src/gl2ps-1.3.8.tgz"
@@ -13,4 +11,40 @@ class Gl2ps < Formula
     system "cmake", ".", *std_cmake_args
     system "make", "install"
   end
+
+  test do
+    (testpath/"test.c").write <<-EOS.undent
+      #include <GLUT/glut.h>
+      #include <gl2ps.h>
+
+      int main(int argc, char *argv[])
+      {
+        glutInit(&argc, argv);
+        glutInitDisplayMode(GLUT_DEPTH);
+        glutInitWindowSize(400, 400);
+        glutInitWindowPosition(100, 100);
+        glutCreateWindow(argv[0]);
+        GLint viewport[4];
+        glGetIntegerv(GL_VIEWPORT, viewport);
+        FILE *fp = fopen("test.eps", "wb");
+        GLint buffsize = 0, state = GL2PS_OVERFLOW;
+        while( state == GL2PS_OVERFLOW ){
+          buffsize += 1024*1024;
+          gl2psBeginPage ( "Test", "Homebrew", viewport,
+                           GL2PS_EPS, GL2PS_BSP_SORT, GL2PS_SILENT |
+                           GL2PS_SIMPLE_LINE_OFFSET | GL2PS_NO_BLENDING |
+                           GL2PS_OCCLUSION_CULL | GL2PS_BEST_ROOT,
+                           GL_RGBA, 0, NULL, 0, 0, 0, buffsize,
+                           fp, "test.eps" );
+          gl2psText("Homebrew Test", "Courier", 12);
+          state = gl2psEndPage();
+        }
+        fclose(fp);
+        return 0;
+      }
+    EOS
+    system ENV.cc, "-lgl2ps", "-framework", "OpenGL", "-framework", "GLUT", "-framework", "Cocoa", "test.c", "-o", "test"
+    system "./test"
+    assert File.exist?("test.eps") && File.size("test.eps") > 0
+  end
 end