autotest: warn if sequential tests are not sent to same parallel worker

autotest/conftest.py

@@ -238,10 +238,36 @@ def pytest_collection_modifyitems(config, items):
                     )
                 )
 
+        # For any tests marked to run sequentially (pytest.mark.random_order(disabled=True)
+        # check to make sure they are also marked with pytest.mark.xdist_group()
+        # so they are sent to the same xdist worker.
+        unmarked_modules = set()
+        xdist = config.pluginmanager.getplugin("xdist")
+        if xdist and xdist.is_xdist_worker(item.session):
+            for mark in item.iter_markers("random_order"):
+                if (
+                    mark.kwargs["disabled"]
+                    and not next(item.iter_markers("xdist_group"), None)
+                    and item.module.__name__ not in unmarked_modules
+                ):
+                    unmarked_modules.add(item.module.__name__)
+                    import warnings
+
+                    warnings.warn(
+                        f"module {item.module.__name__} marked as random_order(disabled=True) but does not have an assigned xdist_group"
+                    )
+
 
 def pytest_addoption(parser):
     parser.addini("gdal_version", "GDAL version for which pytest.ini was generated")
 
+    # our pytest.ini specifies --dist=loadgroup but we don't want to fail if the
+    # user doesn't have this extension installed.
+    try:
+        import xdist  # noqa: F401
+    except ImportError:
+        parser.addoption("--dist")
+
 
 def pytest_configure(config):
     test_version = config.getini("gdal_version")

autotest/utilities/test_gdaltindex.py

@@ -41,6 +41,7 @@
         reason="gdaltindex not available",
     ),
     pytest.mark.random_order(disabled=True),
+    pytest.mark.xdist_group("test_gdaltindex"),
 ]
 
 

autotest/utilities/test_gnmutils.py

@@ -47,6 +47,7 @@
         reason="gnmanalyse not available",
     ),
     pytest.mark.random_order(disabled=True),
+    pytest.mark.xdist_group("test_gnmutils"),
 ]
 
 

cmake/template/pytest.ini.in

@@ -27,6 +27,10 @@ markers =
     require_proj: Skip test(s) if required PROJ version is not available
     require_run_on_demand: Skip test(s) if RUN_ON_DEMAND environment variable is not set
     slow: Skip test(s) if GDAL_RUN_SLOW_TESTS environment variable is not set
+    xdist_group: Associated test with a named group that will be sent to a single parallel worker
 
 # Make sure that all markers are declared above
-addopts = --strict-markers
+# --strict-markers causes an error if a test has a marker that is not handled
+# --dist=loadgroup instructs pytest-xdist to send tests marked with the same
+#                  xdist_group marker to the same worker.
+addopts = --strict-markers --dist=loadgroup