Feature #318 tests for read data files

[John-Sharples]

Changes

• rejig how the test data is handled
• add test for mtd 2d revision
• add data and test for vsdb file

Pull Request Testing

• [x] Describe testing already performed for these changes:
  Test run locally

• [x] Recommend testing for the reviewer(s) to perform, including the location of input datasets, and any additional instructions:
  Nil

• [ ] Do these changes include sufficient documentation updates, ensuring that no errors or warnings exist in the build of the documentation? [Yes or No]

• [x] Do these changes include sufficient testing updates? [Yes or No] Yes

• [x] Will this PR result in changes to the test suite? [Yes or No]
  If yes, describe the new output and/or changes to the existing output:
  Yes, adds tests

• [ ] Do these changes introduce new SonarQube findings? [Yes or No]
  If yes, please describe:

• [ ] Please complete this pull request review by [Fill in date].
  

Pull Request Checklist

See the METplus Workflow for details.

• [ ] Add any new Python packages to the METplus Components Python Requirements table.
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• [ ] Complete the PR definition above.
• [ ] Ensure the PR title matches the feature or bugfix branch name.
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• [ ] After submitting the PR, select the :gear: icon in the Development section of the right hand sidebar. Search for the issue that this PR will close and select it, if it is not already selected.
• [ ] After the PR is approved, merge your changes. If permissions do not allow this, request that the reviewer do the merge.
• [ ] Close the linked issue and delete your feature or bugfix branch from GitHub.