Mixed DML conflict in unit test involving two queueable jobs

Question

I have a complex Apex trigger that calls two separate queueable jobs - one job inserts Permission Set Assignments, and another job creates and deletes ContactShare records. I am positive that neither job can invoke the other via trigger actions.

When I run the unit test, I get a mixed DML error from the second job because of the Permission Set Assignment creation in the first job.

Question: If queued jobs are running within the same startTest/stopTest block, can they cause Mixed DML issues with each other? Is there a workaround for it?

The two jobs are initiated as part of a single Apex transaction (inserting a user). I have the user insertion wrapped in a System.runAs() in the test, and it's in a startTest/stopTest block.

I can see from the debug log that when the first job is executed:

14:39:20.596 (6305771684)|CODE_UNIT_STARTED|[EXTERNAL]|01pK0000000HEBm|DESK_UserDomain
14:39:20.596 (6305842037)|SYSTEM_METHOD_ENTRY|[14]|QueueableContextImpl.QueueableContextImpl()
14:39:20.596 (6305854657)|SYSTEM_METHOD_EXIT|[14]|QueueableContextImpl
14:39:20.596 (6308757099)|DML_BEGIN|[396]|Op:Insert|Type:PermissionSetAssignment|Rows:1

I see the second job starting as well, but there's no reference to QueueableContextImpl.QueueableContextImpl. Does that occur only once and apply to all queuable jobs spawned within the startTest/stopTest block?

14:39:20.596 (6494302250)|CODE_UNIT_STARTED|[EXTERNAL]|01pK0000000HAZp|HL_ClientDataSharing
14:39:20.596 (6496669468)|USER_DEBUG|[464]|### Starting Queued Execution for HL_ClientDataSharing.queueClientDataSharing()

Answer 1

When you call Test.stopTest(), all enqueued asynchronous code runs synchronously. I recommend @TestVisible static Boolean flags to toggle off the Queueable jobs as needed in your test context.

If you are already using a trigger handler framework, it should be dead simple to drop them in. For example, my typical framework would look like:

public with sharing class MyObjectTriggerHandler
{
    // I always include the bypassTrigger flag.

    // It can speed your test suite up tremendously
    // if you implement across the board and use it when you don't need
    // the trigger logic for a particular object to run.

    // It also simplifies testing the service layer
    // when you need the objects to be inserted.
    @TestVisible static Boolean bypassTrigger = false;

    // I would then add these two supplemental flags
    @TestVisible static Boolean assignPermissionSets = true;
    @TestVisible static Boolean createContactShares = true;

    final List<MyObject__c> newRecords;
    final Map<Id, MyObject__c> oldMap;
    public MyObjectTriggerHandler(List<MyObject> newRecords, Map<Id, MyObject__c> oldMap)
    {
        this.newRecords = newRecords;
        this.oldMap = oldMap;
    }

    public void afterInsert()
    {
        if (bypassTrigger) return;

        if (assignPermissionSets) { /*execute permissions job*/}
        if (createContactShares) { /*execute sharing job*/}
    }
}

Then in your test class, you can test each job independently and avoid mixed DML.

static testmethod testInsert_AssignPermissionSets()
{
    MyObjectTriggerHandler.createContactShares = false;
    // set up data

    Test.startTest();
        // execute DML
    Test.stopTest();

    // assert on permissions
}
static testmethod testInsert_CreateContactShares()
{
    MyObjectTriggerHandler.assignPermissionSets = false;
    // set up data

    Test.startTest();
        // execute DML
    Test.stopTest();

    // assert on shares
}