Add test for unbound env variables

[czunker]

This will check the metadata whether the specified env variables really aren't present.

Fixes #281

Signed-off-by: Christian Zunker christian.zunker@codecentric.cloud

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[czunker]

@googlebot I signed it!

[nkubala]

@czunker thank you for the contribution! this change looks good, but I'd like to see tests added for all new additions to the code :)

would you mind adding some tests to the tests/{ARCH}/*_metadata_test.yaml files, e.g. https://github.com/GoogleContainerTools/container-structure-test/blob/master/tests/amd64/ubuntu_20_04_metadata_test.yaml? you should just be able to add small tests using this new field and they should be run as normal in the integration tests.

[czunker]

@nkubala Thanks for the feedback.
I'll have a look at the tests and add them to this PR.

[czunker]

Hi @nkubala ,

tests are present and running tests/structure_test_tests.sh worked out fine.
Please have a look.