tests: Don't assume SDL_Init will leave SDL_GetError unset (py-sdl#258)

SDL_GetError works like Standard C errno: if a call fails it will
(generally) set the error indicator, but if a call succeeds there is no
guarantee about whether the error indicator has been set, cleared, or
left at its previous value.

The SDL documentation says this:

    The message is only applicable when an SDL function has signaled an
    error. You must check the return values of SDL function calls to
    determine when to appropriately call SDL_GetError(). You should not
    use the results of SDL_GetError() to decide if an error has occurred!
    Sometimes SDL will set an error string even when reporting success.

In particular, with a SDL 2.27.x git snapshot, a successful SDL_Init can
leave the error indicator set to a message about inability to open an
input device node, and this does not mean it has failed.

In this commit I have not attempted to check or fix other uses of
SDL_GetError, only the ones that follow SDL_Init. This is enough to make
the test suite pass on Debian 12 alpha with
`SDL_VIDEODRIVER=dummy SDL_AUDIODRIVER=dummy SDL_RENDER_DRIVER=software`
for now, but the other SDL_GetError() calls in the test suite should
ideally also be checked.

Partial solution for: py-sdl#257

Signed-off-by: Simon McVittie <smcv@collabora.com>

sdl2/test/audio_test.py

@@ -23,8 +23,7 @@ def with_sdl_audio():
     sdl2.SDL_Quit()
     sdl2.SDL_ClearError()
     ret = sdl2.SDL_Init(sdl2.SDL_INIT_VIDEO | sdl2.SDL_INIT_AUDIO)
-    assert sdl2.SDL_GetError() == b""
-    assert ret == 0
+    assert ret == 0, sdl2.SDL_GetError().decode('utf-8', 'replace')
     yield
     sdl2.SDL_Quit()
     # Reset original audio driver in environment
@@ -308,7 +307,7 @@ def test_SDL_GetDefaultAudioInfo(with_default_driver):
     # If method isn't implemented for the current back end, just skip
     if ret < 0 and b"not supported" in sdl2.SDL_GetError():
         pytest.skip("not supported by driver")
-    assert ret == 0
+    assert ret == 0, sdl2.SDL_GetError().decode('utf-8', 'replace')
     # Validate frequency and channel count were set
     hz = outspec.freq
     fmt = FORMAT_NAME_MAP[outspec.format] if outspec.format > 0 else 'unknown'

sdl2/test/conftest.py

@@ -13,8 +13,7 @@
 def with_sdl():
     sdl2.SDL_ClearError()
     ret = sdl2.SDL_Init(sdl2.SDL_INIT_VIDEO | sdl2.SDL_INIT_TIMER)
-    assert sdl2.SDL_GetError() == b""
-    assert ret == 0
+    assert ret == 0, sdl2.SDL_GetError().decode('utf-8', 'replace')
     yield
     sdl2.SDL_Quit()
 

sdl2/test/gamecontroller_test.py

@@ -10,7 +10,7 @@
 # Get status of gamepad support/availability before running tests
 SDL_ClearError()
 ret = SDL_Init(sdl2.SDL_INIT_GAMECONTROLLER)
-gamepad_works = ret == 0 and SDL_GetError() == b""
+gamepad_works = ret == 0
 SDL_Quit()
 
 pytestmark = pytest.mark.skipif(not gamepad_works, reason="system unsupported")
@@ -35,8 +35,7 @@ def with_sdl():
     sdl2.SDL_ClearError()
     sdl2.SDL_SetHint(b"SDL_JOYSTICK_ALLOW_BACKGROUND_EVENTS", b"1")
     ret = sdl2.SDL_Init(sdl2.SDL_INIT_VIDEO | sdl2.SDL_INIT_GAMECONTROLLER)
-    assert sdl2.SDL_GetError() == b""
-    assert ret == 0
+    assert ret == 0, sdl2.SDL_GetError().decode('utf-8', 'replace')
     # Also initialize a virtual joystick (if supported)
     if sdl2.dll.version >= 2014:
         virt_type = joystick.SDL_JOYSTICK_TYPE_GAMECONTROLLER

sdl2/test/hints_test.py

@@ -9,8 +9,7 @@
 def with_sdl():
     sdl2.SDL_ClearError()
     ret = sdl2.SDL_Init(sdl2.SDL_INIT_VIDEO)
-    assert sdl2.SDL_GetError() == b""
-    assert ret == 0
+    assert ret == 0, sdl2.SDL_GetError().decode('utf-8', 'replace')
     yield
     sdl2.SDL_Quit()
 

sdl2/test/joystick_test.py

@@ -11,7 +11,7 @@
 any_joysticks = False
 SDL_ClearError()
 ret = SDL_Init(SDL_INIT_JOYSTICK)
-joystick_works = ret == 0 and SDL_GetError() == b""
+joystick_works = ret == 0
 if joystick_works:
     devices = sdl2.SDL_NumJoysticks()
     if sdl2.dll.version >= 2014:
@@ -42,8 +42,7 @@ def with_sdl():
     sdl2.SDL_ClearError()
     sdl2.SDL_SetHint(b"SDL_JOYSTICK_ALLOW_BACKGROUND_EVENTS", b"1")
     ret = sdl2.SDL_Init(sdl2.SDL_INIT_VIDEO | sdl2.SDL_INIT_JOYSTICK)
-    assert sdl2.SDL_GetError() == b""
-    assert ret == 0
+    assert ret == 0, sdl2.SDL_GetError().decode('utf-8', 'replace')
     # Also initialize a virtual joystick (if supported)
     if sdl2.dll.version >= 2014:
         virt_type = sdl2.SDL_JOYSTICK_TYPE_GAMECONTROLLER

sdl2/test/sdl_test.py

@@ -25,7 +25,7 @@ def test_SDL_Init():
         ret = sdl2.SDL_Init(flags)
         err = sdl2.SDL_GetError()
         if name in ['timer', 'audio', 'video', 'events']:
-            assert ret == 0
+            assert ret == 0, err.decode('utf-8', 'replace')
         if err:
             err = err.decode('utf-8')
             print("Error loading {0} subsystem: {1}".format(name, err))
@@ -40,12 +40,11 @@ def test_SDL_Init():
 def test_SDL_InitSubSystem():
     sdl2.SDL_ClearError()
     ret = sdl2.SDL_Init(SDL_INIT_VIDEO | SDL_INIT_AUDIO)
-    assert sdl2.SDL_GetError() == b""
-    assert ret == 0
+    assert ret == 0, sdl2.SDL_GetError().decode('utf-8', 'replace')
     # Test initializing an additional subsystem
     assert sdl2.SDL_WasInit(0) & SDL_INIT_TIMER != SDL_INIT_TIMER
     ret = sdl2.SDL_InitSubSystem(SDL_INIT_TIMER)
-    assert sdl2.SDL_GetError() == b""
+    assert ret == 0, sdl2.SDL_GetError().decode('utf-8', 'replace')
     assert sdl2.SDL_WasInit(0) & SDL_INIT_TIMER == SDL_INIT_TIMER
     # Test shutting down a single subsystem
     sdl2.SDL_QuitSubSystem(SDL_INIT_AUDIO)

sdl2/test/sdlmixer_test.py

@@ -32,8 +32,7 @@ def with_sdl_mixer():
     # Initialize SDL2 with video and audio subsystems
     sdl2.SDL_ClearError()
     ret = sdl2.SDL_Init(sdl2.SDL_INIT_VIDEO | sdl2.SDL_INIT_AUDIO)
-    assert sdl2.SDL_GetError() == b""
-    assert ret == 0
+    assert ret == 0, sdl2.SDL_GetError().decode('utf-8', 'replace')
     # Initialize SDL_mixer and open an audio device
     flags = (
         sdlmixer.MIX_INIT_FLAC | sdlmixer.MIX_INIT_MOD | sdlmixer.MIX_INIT_MP3 |

sdl2/test/sensor_test.py

@@ -19,7 +19,7 @@
 
 def test_SDL_NumSensors():
     ret = SDL_Init(SDL_INIT_SENSOR)
-    assert ret == 0
+    assert ret == 0, sdl2.SDL_GetError().decode('utf-8', 'replace')
     retval = sdl2.SDL_NumSensors()
     SDL_Quit()
     assert retval >= 0

sdl2/test/touch_test.py

@@ -18,8 +18,7 @@ def with_sdl():
     sdl2.SDL_SetHint(sdl2.SDL_HINT_MOUSE_TOUCH_EVENTS, b"1")
     sdl2.SDL_ClearError()
     ret = sdl2.SDL_Init(sdl2.SDL_INIT_VIDEO)
-    assert sdl2.SDL_GetError() == b""
-    assert ret == 0
+    assert ret == 0, sdl2.SDL_GetError().decode('utf-8', 'replace')
     yield
     sdl2.SDL_Quit()
 

sdl2/test/video_test.py

@@ -194,8 +194,7 @@ def test_SDL_VideoInitQuit():
     # Test with default driver
     assert sdl2.SDL_WasInit(0) & sdl2.SDL_INIT_VIDEO != sdl2.SDL_INIT_VIDEO
     ret = sdl2.SDL_VideoInit(None)
-    assert sdl2.SDL_GetError() == b""
-    assert ret == 0
+    assert ret == 0, sdl2.SDL_GetError().decode('utf-8', 'replace')
     assert sdl2.SDL_GetCurrentVideoDriver() # If initialized, should be string
     sdl2.SDL_VideoQuit()
     assert not sdl2.SDL_GetCurrentVideoDriver()