Need tests to show correct handling of input data

There are no tests to show that data read from files is correctly handled.

For example, the bug https://github.com/apache/incubator-ponymail-foal/issues/2 was found by accident rather than by a suitable test.

Also need to show that "From " lines are correctly handled in headers and in message bodies

Start by reviewing the repository's Python unit-test structure and the behavior described in the linked bug, incubator-ponymail-foal issue 2. Add tests showing correct handling of data read from files, including "From " lines in headers and message bodies; done means these cases are covered and regressions are detectable.

Written by the indexing model from the issue text.