Catch testing error and display a more user friendly error message.

[Immutablevoid]

Currently when running npm test you get this error if the Redis server is off:

(node:46320) UnhandledPromiseRejectionWarning: Error: connect ECONNREFUSED 127.0.0.1:6379
    at TCPConnectWrap.afterConnect [as oncomplete] (net.js:1106:14)
(node:46320) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 1)
(node:46320) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

Should catch this error and display a more user friendly error message.

Here is a link that may help jestjs/jest#5311

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I think this issue was mention before, but I couldn't find the issue relating to this one. Can close if it already exist.

[humphd]

See previous discussion in #116 (comment) and #48. CC @aprilllllllll

[aprilllllllll]

Yes, I am working on this.

[humphd]

#494 (comment) is another example of the problem this needs to fix.