Karma Test running after executing tests screen goes blank

The culprit is the client.clearContext option in the Karma configuration :

If true, Karma clears the context window upon the completion of running the tests. If false, Karma does not clear the context window upon the completion of running the tests. Setting this to false is useful when embedding a Jasmine Spec Runner Template.

To avoid blanking the screen, disable this option, like so (karma.conf.js):

module.exports = function (config) {
    config.set({
        /* ... */
        client: {
            clearContext: false
        }
        /* ... */
    })
}