code: def test_fused_blockwise_dataframe_merge(c, fuse):
      pd = pytest.importorskip("pandas")
      dd = pytest.importorskip("dask.dataframe")
  
      # Generate two DataFrames with more partitions than
      # the `max_branch` default used for shuffling (32).
      # We need a multi-stage shuffle to cover #7178 fix.
      size = 35
      df1 = pd.DataFrame({"x": range(size), "y": range(size)})
      df2 = pd.DataFrame({"x": range(size), "z": range(size)})
      ddf1 = dd.from_pandas(df1, npartitions=size) + 10
      ddf2 = dd.from_pandas(df2, npartitions=5) + 10
      df1 += 10
      df2 += 10
  
      with dask.config.set({"optimization.fuse.active": fuse}):
          ddfm = ddf1.merge(
              ddf2, on=["x"], how="left", shuffle_method="tasks"
          )
          ddfm.head()  # https://github.com/dask/dask/issues/7178
          dfm = ddfm.compute().sort_values("x")
          # We call compute above since `sort_values` is not
          # supported in `dask.dataframe`
      dd.utils.assert_eq(
          dfm,
          df1.merge(df2, on=["x"], how="left").sort_values("x"),
          check_index=False,
      )
  
imports: from __future__ import annotations
  import pytest
  import asyncio
  import os
  import sys
  from functools import partial
  from operator import add
  from distributed import Client, SchedulerPlugin, WorkerPlugin
  from distributed.utils_test import cleanup
  from distributed.utils_test import client
  from distributed.utils_test import cluster, cluster_fixture, gen_cluster, loop, loop_in_thread, popen, varying
  import dask
  import dask.bag
  from dask import compute, delayed, persist
  from dask.base import compute_as_if_collection, get_scheduler
  from dask.blockwise import Blockwise
  from dask.delayed import Delayed
  from dask.distributed import futures_of, wait
  from dask.layers import ShuffleLayer, SimpleShuffleLayer
  from dask.utils import get_named_args, get_scheduler_lock, tmpdir, tmpfile
  from dask.utils_test import inc
label_desc: Use image node_id 6 for calling a global function with example usage: test_fused_blockwise_dataframe_merge(c, fuse) without return types