Since Winter 18 update I'm getting the Internal Salesforce Error (-131831505) while executing Unit tests. Seems error persists during tests only. It works okay in real-time. I was able to find out that code fails on Inserting the task with custom Record Type Id which is part of the package:

Task task = new Task(Subject = "Subject",
                                 Description = "Description",
                                 ActivityDate = Date.today(),
                                 RecordTypeId = recordTypeId,
                                 Status = 'Completed'
                                 );

Since Winter 18 update I'm getting the Internal Salesforce Error (-131831505) while executing Unit tests. Seems error persists during tests only. It works okay in real-time. I was able to find out that code fails on Inserting the task with custom Record Type Id which is part of the package:

Task task = new Task(Subject = "Subject",
                                 Description = "Description",
                                 ActivityDate = Date.today(),
                                 RecordTypeId = recordTypeId,
                                 Status = 'Completed'
                                 );