Address duplication in test assertions

[MikeRippon]

We constantly have to assert newline characters, which makes assertions much less readable. Consider something like
assertThat(renderer, rendersLines(
"something",
"something else",
));

This allows future abstraction of how the rendering is performed (eg, rendering to a screen or file, instead of a string?)

Also think about indentation coupling. This is defined in many tests and render classes!