Testing: Unit tests for individual components

[hydrosquall]

Presently, only the root DataExplorer is tested ( see https://github.com/nteract/data-explorer/blob/main/__tests__/index.spec.tsx ).

It will be easier to catch / guard against component specific issues components below the level of the root DataExplorer if we tested specific visuals / components (Plot Picker, etc) individually.

Based on recent bugs, I think it would be valuable to implement basic tests for

• Grid (table) - (e.g. for fix: Correctly display complex datatypes (objects) in table cells #65 )
• Scatterplot (e.g. for Data Explorer: Scatterplot size ignored in Firefox #23)
• Other visualization types as topics arise.

This exercise will also help with writing component specific documentation.

Once this is done in a basic form for a few components, we'll have a good pattern in place that should be easy for new/first time contributors to mimic/add to.