UNIT_RenderingIface_TEST_ogre2_gl3plus test tries to load ogre and fails if it is not able to load it

[traversaro]

Environment

• OS Version: Ubuntu 24.04
• Source or binary build? Source a9af984

Description

The UNIT_RenderingIface_TEST_ogre2_gl3plus fails if gz-rendering is compiled with ogre(1) support but no X server is available, as it actually tries to load ogre(1) plugin in

gz-rendering/test/common_test/RenderingIface_TEST.cc

Lines 126 to 133 in a9af984

	RenderEngine *eng = engine(0u);
	ASSERT_NE(nullptr, eng);
	auto engineName = eng->Name();
	ASSERT_FALSE(engineName.empty());
	EXPECT_TRUE(hasEngine(engineName));
	EXPECT_NO_THROW(unregisterEngine(0u));
	EXPECT_FALSE(hasEngine(engineName));

as it select the engine with index 0, that is ogre1.

Expected behavior:

I would expect that even if no X server is available (and so ogre plugin can't work), DISPLAY= ctest -VV -E "_ogre_" would be able to run.

Actual behavior:

With DISPLAY= ctest -VV -E "_ogre_" all tests pass fine, except for UNIT_RenderingIface_TEST_ogre2_gl3plus.

Steps to reproduce

You can see that UNIT_RenderingIface_TEST_ogre2_gl3plus fails if there is no X server by running it by setting DISPLAY to an empty variable

1. DISPLAY= ctest -VV -R UNIT_RenderingIface_TEST_ogre2_gl3plus

Output

Running main() from /home/conda/feedstock_root/build_artifacts/gz-rendering8_1727901808682/work/test/gtest_vendor/src/gtest_main.cc
[==========] Running 3 tests from 1 test suite.
[----------] Global test environment set-up.
[----------] 3 tests from RenderingIfaceTest
[ RUN      ] RenderingIfaceTest.HasEngine
[       OK ] RenderingIfaceTest.HasEngine (0 ms)
[ RUN      ] RenderingIfaceTest.GetEngine
[Wrn] [Ogre2RenderEngine.cc:548] Unable to open display: . Trying to run in headless mode.
[Err] [RenderEngineManager.cc:484] Failed to load plugin [no_such_engine] : couldn't find shared library.
[Err] [RenderEngineManager.cc:231] Invalid render-engine index: 1000000
[Dbg] [CommonRenderingTest.hh:44] Read GZ_ENGINE_TO_TEST=ogre2
[Dbg] [CommonRenderingTest.hh:47] Read GZ_ENGINE_BACKEND=gl3plus
[Dbg] [RenderingIface.cc:135] No rendering engine is loaded yet
[Msg] Loading plugin [gz-rendering-ogre2]
[Dbg] [RenderingIface.cc:135] No rendering engine is loaded yet
[Msg] Loading plugin [no_such_engine]
[       OK ] RenderingIfaceTest.GetEngine (283 ms)
[ RUN      ] RenderingIfaceTest.RegisterEngine
[Err] [OgreRenderEngine.cc:358] Unable to open display: 
[Err] [OgreRenderEngine.cc:469] Unable to load Ogre Plugin[/home/conda/feedstock_root/build_artifacts/gz-rendering8_1727901808682/_h_env_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placehold_placeho/lib/OGRE/RenderSystem_GL]. Rendering will not be possible.Make sure you have installed OGRE properly.
[Err] [OgreRenderEngine.cc:512] unable to find OpenGL rendering system. OGRE is probably installed incorrectly. Double check the OGRE cmake output, and make sure OpenGL is enabled.

[traversaro]

I give a quick shot to fix this, but using the engine name in engine/unregisterEngine does not work, and I could not find any way to quickly associate the ogre2 string to the corresponding registered engine index.