Save previous expected files for testing

[forsyth2]

It may be beneficial to save previous expected images/files, as is done in E3SM Diags: https://e3sm-project.github.io/e3sm_diags/_build/html/master/dev_guide/testing.html

Currently, /lcrc/group/e3sm/public_html/zppy_test_resources contains the following:

• expected_bash_files
• expected_complete_run
• expected_environment_commands
• image_list_expected_complete_run.txt
• image_list_expected_environment_commands.txt

The E3SM Diags integration test directory /lcrc/group/e3sm/public_html/e3sm_diags_test_data/integration/expected contains the following:

• integration_test_images, the current expected images
• previous_output
  • integration_test_images_<version>_<date>_<hash>
• README.md containing the version, date, hash for the current expected images.

(/lcrc/group/e3sm/public_html/e3sm_diags_test_data/unit_test_complete_run/expected has a similar setup).

Options:

• Move the current contents of /lcrc/group/e3sm/public_html/zppy_test_resources into /lcrc/group/e3sm/public_html/zppy_test_resources/expected and put all previous output in /lcrc/group/e3sm/public_html/zppy_test_resources/previous_expected. The README listing the version/date/hash could be placed in /lcrc/group/e3sm/public_html/zppy_test_resources/.
• Have subdirectories for each of the three integration tests in /lcrc/group/e3sm/public_html/zppy_test_resources, each with their own READMEs and expected/previous_expected directories.

Note that any changes to the directory structure will require updating the paths in the tests. Run git grep "/lcrc/group/e3sm/public_html/zppy_test_resources" in zppy/tests/integration to find these references.

Documentation on testing would also have to be updated to reflect the process for updating expected files.

[forsyth2]

As of #604, we have scripts for generating archives of expected results.