[SPARK-47499][PYTHON][CONNECT][TESTS] Enable test_help_command test

### What changes were proposed in this pull request?
Reuse `test_help_command` in Connect

### Why are the changes needed?
for test coverage

I checked [SPARK-5464](https://issues.apache.org/jira/browse/SPARK-5464) that it seems doesn't have to create this test dataframe from python RDD

### Does this PR introduce _any_ user-facing change?
no, test-only

### How was this patch tested?
ci

### Was this patch authored or co-authored using generative AI tooling?
no

Closes apache#45634 from zhengruifeng/reuse_test_help.

Authored-by: Ruifeng Zheng <[email protected]>
Signed-off-by: Dongjoon Hyun <[email protected]>

python/pyspark/sql/tests/connect/test_parity_dataframe.py

@@ -22,9 +22,9 @@
 
 
 class DataFrameParityTests(DataFrameTestsMixin, ReusedConnectTestCase):
-    @unittest.skip("Spark Connect does not support RDD but the tests depend on them.")
     def test_help_command(self):
-        super().test_help_command()
+        df = self.spark.createDataFrame(data=[{"foo": "bar"}, {"foo": "baz"}])
+        super().check_help_command(df)
 
     # Spark Connect throws `IllegalArgumentException` when calling `collect` instead of `sample`.
     def test_sample(self):

python/pyspark/sql/tests/test_dataframe.py

@@ -139,6 +139,9 @@ def test_help_command(self):
         rdd = self.sc.parallelize(['{"foo":"bar"}', '{"foo":"baz"}'])
         df = self.spark.read.json(rdd)
         # render_doc() reproduces the help() exception without printing output
+        self.check_help_command(df)
+
+    def check_help_command(self, df):
         pydoc.render_doc(df)
         pydoc.render_doc(df.foo)
         pydoc.render_doc(df.take(1))