Output integration test needed

[ross-spencer]

The Python 3 work is close to being finished. String handling in output is not ideal but it works - a refactor and rethinking of how the output is achieved should happen in the near future. Integration tests from this perspective are to ensure that data is output without error and maybe some basic content checks, e.g. for specific headers? But primarily, Unicode/string handling errors are the biggest risk here so making sure they aren't triggered using some of the depth of test-data we've created will make a difference.