Add better Paragraph/Text/Line/Span style tests

[joshka]

Problem

The addition of Text::style and Line::style broke some assumptions about how things should work in Paragraph.

We need a comprehensive set of tests that shows how the following styles interact:

• Any existing background style that is rendered to the buffer beforehand
• Paragraph::style
• Block::style
• Text::style
• Line::style
• Span::style

Solution

• Add an integration test for this under the tests/ folder that tests the combinations. A good name for this might be tests/text_style.rs?
• Check whether the unit tests cover this from the perspective of the individual types and make the tests consistent and simple. A good way to do this would be to have a style module in the tests module in each of the paragraph.rs/text.rs/... files.
• Ensure the API docs for each of the items indicate the expected interactions neatly (e.g. <this style> overrides <that style>)
• Ensure that any illogical overrides / bugs are fixed (note that these might be bugs in the docs or bugs in the implementation. It's important to discuss and capture the rationale / intent behind these before fixing the inconsistencies.

Alternatives

Additional context

• refactor: visitor method to process paragraph wrapped text #956 (comment) (documents a possible bug that wasn't fixed by fix: ensure that paragraph correctly renders styled text #992)
• fix: ensure that paragraph correctly renders styled text #992 (attempted to fix the Paragraph bug)

[akshay1992kalbhor]

Can I take this one?

[joshka]

Can I take this one?

Sure!

[joshka]

I added some detail to the solution suggestions. I want to re-iterate that the primary goals on this issue are to ensure that we are rendering these things consistently and correctly and to make that clear with both docs and tests.