[CI] Fix gpu deps import in cpu test (#21950)

python/sglang/test/test_utils.py

@@ -2056,6 +2056,44 @@ def _distributed_worker(rank, world_size, backend, port, func, result_queue, kwa
         dist.destroy_process_group()
 
 
+def maybe_stub_sgl_kernel():
+    """Stub sgl_kernel if it cannot be imported (e.g. no GPU).
+
+    Must be called before any import that transitively depends on sgl_kernel.
+    On machines with a working sgl_kernel this is a no-op.
+    """
+    try:
+        import sgl_kernel  # noqa: F401
+
+        return
+    except (ImportError, OSError):
+        pass
+
+    import importlib.abc
+    import importlib.machinery
+
+    class _SglKernelLoader(importlib.abc.Loader):
+        def create_module(self, spec):
+            return None
+
+        def exec_module(self, module):
+            from unittest.mock import MagicMock
+
+            module.__getattr__ = lambda name: MagicMock()
+
+    class _SglKernelFinder(importlib.abc.MetaPathFinder):
+        def find_spec(self, fullname, path, target=None):
+            if fullname == "sgl_kernel" or fullname.startswith("sgl_kernel."):
+                return importlib.machinery.ModuleSpec(
+                    fullname,
+                    _SglKernelLoader(),
+                    is_package=True,
+                )
+            return None
+
+    sys.meta_path.insert(0, _SglKernelFinder())
+
+
 class CustomTestCase(unittest.TestCase):
 
     def __init_subclass__(cls, **kwargs):