Cached plugin descriptors hold a reference on the plugin options, which break if the plugin options object is replaced. That case happens when the user updates the plugin options with a new object, but also since the new config update logic (#4198) that now always clones the plugin options. The fix consists in explicitly invalidating that cache before updating the chart.
`karma.conf.ci.js` has been merged into `karma.conf.js` for local testing consistency: `gulp unittestWatch` has been replaced by `gulp unittest --watch` and thus use exactly the same config file. Upgrade to latest jasmine and karma packages and remove deprecated `gulp-karma` dependency (directly use `karma.Server` in gulp).
Split `test/mockContext.js` into smaller `test/jasmine.*` modules to make easier unit tests maintenance and finally, move all `*.test.js` files under the `test/specs` folder.
