FindGIF: Add test

This tests whether GIFLIB can be found and the linker works. For newer
versions (>=5) it also tests if the version was parsed correctly.

Tests/CMakeLists.txt

@@ -1388,6 +1388,10 @@ ${CMake_BINARY_DIR}/bin/cmake -DDIR=dev -P ${CMake_SOURCE_DIR}/Utilities/Release
     add_subdirectory(FindGDAL)
   endif()
 
+  if(CMake_TEST_FindGIF)
+    add_subdirectory(FindGIF)
+  endif()
+
   if(CMake_TEST_FindGSL)
     add_subdirectory(FindGSL)
   endif()

Tests/FindGIF/CMakeLists.txt

@@ -0,0 +1,10 @@
+add_test(NAME FindGIF.Test COMMAND
+  ${CMAKE_CTEST_COMMAND} -C $<CONFIGURATION>
+  --build-and-test
+  "${CMake_SOURCE_DIR}/Tests/FindGIF/Test"
+  "${CMake_BINARY_DIR}/Tests/FindGIF/Test"
+  ${build_generator_args}
+  --build-project TestFindGIF
+  --build-options ${build_options}
+  --test-command ${CMAKE_CTEST_COMMAND} -V -C $<CONFIGURATION>
+  )

Tests/FindGIF/Test/CMakeLists.txt

@@ -0,0 +1,16 @@
+cmake_minimum_required(VERSION 3.4)
+project(TestFindGIF C)
+include(CTest)
+
+find_package(GIF REQUIRED)
+
+add_definitions(-DCMAKE_EXPECTED_GIF_VERSION="${GIF_VERSION}")
+
+add_executable(test_tgt main.c)
+target_link_libraries(test_tgt GIF::GIF)
+add_test(NAME test_tgt COMMAND test_tgt)
+
+add_executable(test_var main.c)
+target_include_directories(test_var PRIVATE ${GIF_INCLUDE_DIRS})
+target_link_libraries(test_var PRIVATE ${GIF_LIBRARIES})
+add_test(NAME test_var COMMAND test_var)

Tests/FindGIF/Test/main.c

@@ -0,0 +1,35 @@
+#include <assert.h>
+#include <stdio.h>
+#include <string.h>
+
+#include <gif_lib.h>
+
+// GIFLIB before version 5 didn't know this macro
+#ifndef GIFLIB_MAJOR
+#  define GIFLIB_MAJOR 4
+#endif
+
+int main()
+{
+  // because of the API changes we have to test different functions depending
+  // on the version of GIFLIB
+#if GIFLIB_MAJOR >= 5
+  // test the linker
+  GifErrorString(D_GIF_SUCCEEDED);
+
+  // check the version
+  char gif_version_string[16];
+  snprintf(gif_version_string, 16, "%i.%i.%i", GIFLIB_MAJOR, GIFLIB_MINOR,
+           GIFLIB_RELEASE);
+
+  assert(strcmp(gif_version_string, CMAKE_EXPECTED_GIF_VERSION) == 0);
+#else
+  // test the linker
+  GifLastError();
+
+  // unfortunately there is no way to check the version in older version of
+  // GIFLIB
+#endif
+
+  return 0;
+}