custom setting error when test classes run in parallel

Question

I have a few test classes that fail but only when all the test classes are run in parallel.I'm using a hierarchy custom setting as part of the test code. In order to narrow down the problem I have the following in my test code:

My_Setting__c settings = My_Setting__c.getOrgDefaults();
settings.some_app_date__c = System.today()+1;
upsert settings;

Ctl_SomePage ctrl = new Ctl_SomePage();
My_Setting__c settings1 = My_setting__c.getOrgDefaults();
system.assert(false,'date: ' + settings1.some_app_date__c);

When run by itself or with parallel disabled this produces a date:

System.AssertException: Assertion Failed: date: 2016-03-01 00:00:00

When run with all tests and parallel enabled I get:

System.DmlException: Upsert failed. First exception on row 0; first error: DUPLICATE_VALUE, duplicate value found: SetupOwnerId duplicates value on record with id: 00DP0000003oTNU: []

If I try to just log out the custom setting its just an empty object. It seems like it won't let me update it but if I try to get the values from it, its empty...

Any suggestions?

Answer 1

Just an example of how mocking could work (based on @kurunve's comment):

public class MySettingMock
{
    @TestVisible static Date mockSettingDate;
    public static Date getOrgWideDefaultDate()
    {
        return Test.isRunningTest() ? mockSettingDate :
            My_Setting__c.getOrgDefaults().Date_To_Mock__c;
    }
    public static void setOrgWideDefaultDate(Date value)
    {
        My_Setting__c defaults = My_Setting__c.getOrgDefaults();
        defaults.Date_To_Mock__c = value;
        if (Test.isRunningTest()) { mockSettingDate = value; }
        else { upsert mockSettingDate; }
    }
}

The way the above is structured, the only line you can't hit from a test is the upsert operation. I haven't tried it myself, but it's an interesting idea. It doesn't scale especially well if you have a bunch of values to work with, but there could be workarounds for that.