Tests: Update PanelColor component unit tests

[gziolo]

Description

Follow up for #3776.

@hideokamoto this is what I had on my mind when I said:

I feel like one snapshot test would be enough here. The second test could only validate if the title is set properly.

It turned out that color is optional rather than the title. Let me know what do you think.

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows has proper inline documentation.

[hideokamoto]

It looks like good for us :)
But I'm wandering about the snapshot returns undefined.
https://github.com/WordPress/gutenberg/pull/3797/files#diff-c01265ef188886c68e8d3a6fe8b1748cR12

Is it correctry behavior ?
Thanks !

[gziolo]

Yes, see this line:

gutenberg/components/panel/color.js

Line 13 in 4a34830

colorValue && <span className="components-panel__color-area" key="color" style={ { background: colorValue } } />,

. When colorValue is not provided it should return undefined. The 2nd test verifies the case when colorValue is provided. We could do the opposite, but I don't feel confident about checking if something is not present :)