Visualization Library Testing Infrastructure changes

Closes #1914, #1915, #1916, #1917, #1918, #1919, #1920, and #1921.

Adding fixtures, mock data, and tests to the visualization library.

This pull request updates the code coverage in the visualization library. There are currently 4 files in the yellow and 2 files in the red. Four of these files (2 red and 2 yellow) will be in the green as soon as we get in unit tests for the Tile Map. The other 2 (yellow) are the legend and dispatch unit tests. Tests were added in the pull requests, however, this still did not bring them into the green. The reason is that we need to find a way to simulate click, brush, and mouse events in order to test the remaining functionality. I will work on adding to these tests in another pull request.
you can use expect(chart.draw()).to.be.a(Function) here