Document GPU plan assertion callback

Signed-off-by: Allen Xu <allxu@nvidia.com>

Author: wjxiz1992

integration_tests/src/main/python/asserts.py

@@ -505,6 +505,16 @@ def assert_cpu_and_gpu_are_equal_collect_with_capture(func,
         conf={},
         require_non_empty=False,
         gpu_plan_assertion=None):
+    """Compare collected CPU/GPU results and validate the executed GPU plan.
+
+    :param func: Function that creates the dataframe to collect in each Spark session.
+    :param exist_classes: Comma-separated class names required in the GPU plan.
+    :param non_exist_classes: Comma-separated class names forbidden in the GPU plan.
+    :param conf: Spark configuration used for both executions.
+    :param require_non_empty: Require the collected CPU result to contain at least one row.
+    :param gpu_plan_assertion: Optional callback invoked after GPU collection with the
+        dataframe's executed JVM plan.
+    """
     (bring_back, collect_type) = _prep_func_for_compare(func, 'COLLECT_WITH_DATAFRAME')
 
     conf = _prep_incompat_conf(conf)