Session06 - HTML Renderer and Tests

Whenever possible and practical it's best to minimize the number of units (classes, methods, and functions) being used in a unit test. This test requires three methods of the `Element()` class to be functioning correctly for it to pass. It's testing that the `__init__()` creates an instance of the class with the default attributes, that `.append()` will accept a string and that `.render()` will write the tags, strings, and indentation in the desired manner. If this test fails you'll need to look for the failure in multiple units; if a more tightly scoped test fails you'll know exactly where the problem is.

Consider splitting this into at least three tests: One that tests the creation of an instance of a class, one that tests the append method, and one that tests the render method.