pytest always creates the .cache directory even when the cache functionality is not used

[svetlin-mladenov]

pytest creates the .cache directory even when no tests are actually executed and the cache functionality is not used at all. In a sense the user pays for what they are not using.

Here is an example where no tests are actually run:

rm .cache/ -rf
truncate empty.py --size 0
py.test empty.py # warns that no tests were run
ls -lad .cache # suprise !

In this example only a single empty test is run but still .cache is created:

rm .cache/ -rf
echo -e "def test_minimal():\n    pass" > minimal.py
py.test minimal.py
ls -lad .cache # suprise !

This issue is clearly related to issue #1029 but is not limited to read-only file systems.