## What changes were proposed in this pull request?
This PR continues to break down a big large file into smaller files. See https://github.com/apache/spark/pull/23021. It targets to follow https://github.com/numpy/numpy/tree/master/numpy.
Basically this PR proposes to break down `pyspark/streaming/tests.py` into ...:
```
pyspark
├── __init__.py
...
├── streaming
│ ├── __init__.py
...
│ ├── tests
│ │ ├── __init__.py
│ │ ├── test_context.py
│ │ ├── test_dstream.py
│ │ ├── test_kinesis.py
│ │ └── test_listener.py
...
├── testing
...
│ ├── streamingutils.py
...
```
## How was this patch tested?
Existing tests should cover.
`cd python` and .`/run-tests-with-coverage`. Manually checked they are actually being ran.
Each test (not officially) can be ran via:
```bash
SPARK_TESTING=1 ./bin/pyspark pyspark.tests.test_context
```
Note that if you're using Mac and Python 3, you might have to `OBJC_DISABLE_INITIALIZE_FORK_SAFETY=YES`.
Closes#23034 from HyukjinKwon/SPARK-26035.
Authored-by: hyukjinkwon <gurwls223@apache.org>
Signed-off-by: hyukjinkwon <gurwls223@apache.org>