Add testdata as tar.gz

[felixcremer]

This adds a small subset of 51 by 70 pixels in the same folder structure as the original Sentinel-1 data. So that we could test and precompile the full function

[meggart]

Should we really add this file to this repo or rather push it to a new repo and make an artifact from it?

[felixcremer]

If there is an easy way to produce an artifact, that would be better than adding this here.

[schlichtanders]

It is only <700 KB
I think it is easier if it is directly part of the repository so that it is automatically versioned (and there is no need to match versions)

[meggart]

It is only <700 KB
I think it is easier if it is directly part of the repository so that it is automatically versioned (and there is no need to match versions)

Sorry, saw this comment too late and had already prepared the artifact. We discussed this also offline and it seems @felixcremer also considers moving to larger test data sizes in the future so we decided to go for the artifacts from the start.

[felixcremer]

The idea is, that with the extra repository we can add more testdata later on as needed and there should be not much versxion problems, because we are only going to add more testdata and not remove it from the testdata folder, so we can simply use the latest artifact from the testdata repository.

[schlichtanders]

if testdata is never going to change, only added, no versioning is needed
but in case testdata changes, it is not possible to link to "latest" testdata, but you need to pin the testdata version so that when going back in git history you still have functional tests.

That is fine of course to pin respective testdata versions (e.g. by commit or time).