Decide how to write unit tests for writer/pango-markup

[cxw42]

It currently has many private functions. I would like to test them since many are not trivial. I can think of several options; any suggestions? Other alternatives I haven't thought of?

• MethodObject: refactor the complex functions into smaller classes
• Write the test code in src/writer alongside the code being tested
• Give more symbols package visibility and move the t/ files into the package where necessary
• Make all those functions public (not preferred)