expressions.tdml exists in daffodil-core.

An extended more elaborate one is in daffodil-test. But I think there are a number of duplicate tests.

If these tests are truly duplicates, then it's just legacy that they are in both places. they should be dropped from daffodil-core, and expressions.tdml removed from daffodil-core.

Alternatively, very basic tests that count as "expressions unit tests" can stay, but duplicates should then be removed from daffodil-test's expressions.tdml so that we don't have a regression causing two identical tests to fail in two places.