Tests added to bring async.js's coverage to 100%.
Tests added to bring async.js's coverage to 100%.

adamryman/splunk-sdk-javascript,splunk/splunk-sdk-javascript,splunk/splunk-sdk-javascript,lowtalker/splunk-sdk-javascript,lowtalker/splunk-sdk-javascript,splunk/splunk-sdk-javascript,adamryman/splunk-sdk-javascript