Adding even more test crumbs

[john-science]

What is the change?

Added test crumbs for:

• cases
• materials

And added impl and test crumbs for:

• database3
• snapshots
• uniform mesh converter
• axial expansion changer

Why is the change being made?

This is part of the on-going requirements work.

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Checklist

• This PR has only one purpose or idea.
• Tests have been added/updated to verify that the new/changed code works.

• The code style follows good practices.
• The commit message(s) follow good practices.

• The release notes (location doc/release/0.X.rst) are up-to-date with any important changes.
• The documentation is still up-to-date in the doc folder.
• No requirements were altered.
• The dependencies are still up-to-date in pyproject.toml.

[john-science]

@bdlafleur @albeanth Just FYI.

[albeanth]

Took a quick glance at the converters package. Just 1 edit. Thanks, @john-science!