Salesforce Run Tests Stuck on HttpCalloutMock Classes



I tried running all tests in my Salesforce workspace. However, execution halted when all five threads got stuck on mock classes that were annotated with @isTest as shown in the docs.

Is this a fluke? Or is there a workaround for this problem in C9? I don’t have this problem running tests directly in Salesforce or in other IDEs (MavensMate, The Welkin Suite).