[SPARK-32783][DOCS][PYTHON] Development - Testing PySpark

### What changes were proposed in this pull request?

This PR proposes to add a page to describe how to test PySpark. Note that it avoids duplication of https://spark.apache.org/developer-tools.html and it more aims to add put the relevant links together.

I made a demo site to review more effectively: https://hyukjin-spark.readthedocs.io/en/stable/development/testing.html

### Why are the changes needed?

To guide PySpark developers easily test.

### Does this PR introduce _any_ user-facing change?

Yes, it will adds a new documentation page.

### How was this patch tested?

Manually tested.

Closes #29634 from HyukjinKwon/SPARK-32783.

Authored-by: HyukjinKwon <[email protected]>
Signed-off-by: HyukjinKwon <[email protected]>

python/docs/source/development/index.rst

@@ -23,4 +23,4 @@ Development
     :maxdepth: 2
 
     contributing
-
+    testing

python/docs/source/development/testing.rst

@@ -0,0 +1,57 @@
+..  Licensed to the Apache Software Foundation (ASF) under one
+    or more contributor license agreements.  See the NOTICE file
+    distributed with this work for additional information
+    regarding copyright ownership.  The ASF licenses this file
+    to you under the Apache License, Version 2.0 (the
+    "License"); you may not use this file except in compliance
+    with the License.  You may obtain a copy of the License at
+
+..    http://www.apache.org/licenses/LICENSE-2.0
+
+..  Unless required by applicable law or agreed to in writing,
+    software distributed under the License is distributed on an
+    "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+    KIND, either express or implied.  See the License for the
+    specific language governing permissions and limitations
+    under the License.
+
+===============
+Testing PySpark
+===============
+
+In order to run PySpark tests, you should build Spark itself first via Maven or SBT. For example,
+
+.. code-block:: bash
+
+    build/mvn -DskipTests clean package
+
+After that, the PySpark test cases can be run via using ``python/run-tests``. For example,
+
+.. code-block:: bash
+
+    python/run-tests --python-executable=python3
+
+Note that you may set ``OBJC_DISABLE_INITIALIZE_FORK_SAFETY`` environment variable to ``YES`` if you are running tests on Mac OS.
+
+Please see the guidance on how to `build Spark <https://github.com/apache/spark#building-spark>`_,
+`run tests for a module, or individual tests <https://spark.apache.org/developer-tools.html>`_.
+
+
+Running Individual PySpark Tests
+--------------------------------
+
+You can run a specific test via using ``python/run-tests``, for example, as below:
+
+.. code-block:: bash
+
+    python/run-tests --testnames pyspark.sql.tests.test_arrow
+
+Please refer to `Testing PySpark <https://spark.apache.org/developer-tools.html>`_ for more details.
+
+
+Running tests using GitHub Actions
+----------------------------------
+
+You can run the full PySpark tests by using GitHub Actions in your own forked GitHub
+repositry with a few clicks. Please refer to
+`Running tests in your forked repository using GitHub Actions <https://spark.apache.org/developer-tools.html>`_ for more details.