Add initial support for running tests offscreen

Makes

    QT_QPA_PLATFORM=offscreen pytest

pass.

See #4914

misc/requirements/requirements-tests.txt

@@ -50,7 +50,7 @@ pytest-qt==4.4.0
 pytest-repeat==0.9.3
 pytest-rerunfailures==15.0
 pytest-xdist==3.6.1
-pytest-xvfb==3.0.0
+pytest-xvfb==3.1.1
 PyVirtualDisplay==3.0
 requests==2.32.3
 requests-file==2.1.0

pytest.ini

@@ -19,6 +19,7 @@ markers =
     not_frozen: Tests which can't be run if sys.frozen is True.
     not_flatpak: Tests which can't be run if running with Flatpak.
     no_xvfb: Tests which can't be run with Xvfb.
+    no_offscreen: Tests which can't be run with the offscreen platform plugin.
     frozen: Tests which can only be run if sys.frozen is True.
     integration: Tests which test a bigger portion of code
     end2end: End to end tests which run qutebrowser as subprocess
@@ -82,7 +83,10 @@ qt_log_ignore =
     # Qt 6.9 Beta 1-3 with Xvfb
     ^Backend texture is not a Vulkan texture\.$
     # With offscreen platform plugin
-    ^This plugin does not support (raise|propagateSizeHints)\(\)$
+    ^This plugin does not support (raise\(\)|propagateSizeHints\(\)|createPlatformVulkanInstance|grabbing the keyboard)$
+    ^QRhiGles2: Failed to create (temporary )?context$
+    ^QVulkanInstance: Failed to initialize Vulkan$
+    ^Unable to detect GPU vendor\.$
 xfail_strict = true
 filterwarnings =
     error

tests/conftest.py

@@ -104,6 +104,10 @@ def _apply_platform_markers(config, item):
          pytest.mark.skipif,
          testutils.ON_CI,
          "Skipped on CI."),
+        ('no_offscreen',
+         pytest.mark.skipif,
+         testutils.offscreen_plugin_enabled(),
+         "Skipped with offscreen platform plugin."),
         ('unicode_locale',
          pytest.mark.skipif,
          sys.getfilesystemencoding() == 'ascii',
@@ -317,10 +321,19 @@ def pytest_report_header(config):
 
 @pytest.fixture(scope='session', autouse=True)
 def check_display(request):
-    if utils.is_linux and not os.environ.get('DISPLAY', ''):
+    if (
+        utils.is_linux
+        and not os.environ.get("DISPLAY", "")
+        and not testutils.offscreen_plugin_enabled()
+    ):
         raise RuntimeError("No display and no Xvfb available!")
 
 
+def pytest_xvfb_disable() -> bool:
+    """Disable Xvfb if the offscreen plugin is in use."""
+    return testutils.offscreen_plugin_enabled()
+
+
 @pytest.fixture(autouse=True)
 def set_backend(monkeypatch, request):
     """Make sure the backend global is set."""

tests/end2end/features/tabs.feature

@@ -1551,7 +1551,7 @@ Feature: Tab management
         And I run :tab-take 0/1
         Then the error "Can't take tabs when using windows as tabs" should be shown
 
-    @windows_skip
+    @windows_skip @no_offscreen
     Scenario: Close the last tab of a window when taken by another window
         Given I have a fresh instance
         When I open data/numbers/1.txt
@@ -1633,7 +1633,7 @@ Feature: Tab management
         And I run :tab-give 0
         Then the error "Can't give tabs when using windows as tabs" should be shown
 
-    @windows_skip
+    @windows_skip @no_offscreen
     Scenario: Close the last tab of a window when given to another window
         Given I have a fresh instance
         When I open data/numbers/1.txt

tests/helpers/testutils.py

@@ -323,6 +323,12 @@ SOFTWARE_RENDERING_FLAG = "--disable-gpu"
 SOFTWARE_RENDERING_ARGS = ["-s", "qt.force_software_rendering", "chromium"]
 
 
+def offscreen_plugin_enabled() -> bool:
+    """Check whether offscreen rendering is enabled."""
+    # FIXME allow configuring via custom CLI flag?
+    return os.environ["QT_QPA_PLATFORM"] == "offscreen"
+
+
 def use_software_rendering() -> bool:
     """Check whether to enforce software rendering for tests."""
     if not _has_qtwebengine():
@@ -333,6 +339,7 @@ def use_software_rendering() -> bool:
         # https://github.com/qutebrowser/qutebrowser/issues/8444#issuecomment-2569554046
         # not on CI, but unknown how to tell apart affected / unaffected systems
         versions.webengine == utils.VersionNumber(6, 9)
+        or offscreen_plugin_enabled()
     )