### What changes were proposed in this pull request?
There are still naming related to Koalas in test and function name. This PR addressed them to fit pandas-on-spark.
- kdf -> psdf
- kser -> psser
- kidx -> psidx
- kmidx -> psmidx
- to_koalas() -> to_pandas_on_spark()
### Why are the changes needed?
This is because the name Koalas is no longer used in PySpark.
### Does this PR introduce _any_ user-facing change?
`to_koalas()` function is renamed to `to_pandas_on_spark()`
### How was this patch tested?
Tested in local manually.
After changing the related naming, I checked them one by one.
Closes#32516 from itholic/SPARK-35364.
Authored-by: itholic <haejoon.lee@databricks.com>
Signed-off-by: Takuya UESHIN <ueshin@databricks.com>
### What changes were proposed in this pull request?
Consolidate PySpark testing utils by removing `python/pyspark/pandas/testing`, and then creating a file `pandasutils` under `python/pyspark/testing` for test utilities used in `pyspark/pandas`.
### Why are the changes needed?
`python/pyspark/pandas/testing` hold test utilites for pandas-on-spark, and `python/pyspark/testing` contain test utilities for pyspark. Consolidating them makes code cleaner and easier to maintain.
Updated import statements are as shown below:
- from pyspark.testing.sqlutils import SQLTestUtils
- from pyspark.testing.pandasutils import PandasOnSparkTestCase, TestUtils
(PandasOnSparkTestCase is the original ReusedSQLTestCase in `python/pyspark/pandas/testing/utils.py`)
Minor improvements include:
- Usage of missing library's requirement_message
- `except ImportError` rather than `except`
- import pyspark.pandas alias as `ps` rather than `pp`
### Does this PR introduce _any_ user-facing change?
No.
### How was this patch tested?
Unit tests under python/pyspark/pandas/tests.
Closes#32177 from xinrong-databricks/port.merge_utils.
Authored-by: Xinrong Meng <xinrong.meng@databricks.com>
Signed-off-by: Takuya UESHIN <ueshin@databricks.com>
### What changes were proposed in this pull request?
Now that we merged the Koalas main code into the PySpark code base (#32036), we should port the Koalas miscellaneous unit tests to PySpark.
### Why are the changes needed?
Currently, the pandas-on-Spark modules are not tested fully. We should enable miscellaneous unit tests.
### Does this PR introduce _any_ user-facing change?
No.
### How was this patch tested?
Enable miscellaneous unit tests.
Closes#32152 from xinrong-databricks/port.misc_tests.
Lead-authored-by: xinrong-databricks <47337188+xinrong-databricks@users.noreply.github.com>
Co-authored-by: Xinrong Meng <xinrong.meng@databricks.com>
Signed-off-by: HyukjinKwon <gurwls223@apache.org>
