Best Practice for testing with RunAs method

Question

I noticed that when you create a user in a test class that the username must be unique in the real production environment. Most of my test classes are creating a user to then run the test method as.

The problem arises from the fact that you can create a test class, deploy it to production, and then have it break by someone else, coincidentally using that same username. Is there a best practice to avoid this besides trying to create long random usernames? Should we query for a random user in the org of that profile?

Answer 1

With following combination to generate unique Username, there were no errors while using runAs with deployments:

public static User createTestUser(Id roleId, Id profID, String fName, String lName) {
    String orgId = UserInfo.getOrganizationId();
    String dateString = String.valueof(Datetime.now())
        .replace(' ','').replace(':','').replace('-','');
    Integer randomInt = Integer.valueOf(math.rint(math.random()*1000000));
    String uniqueName = orgId + dateString + randomInt;
    User tuser = new User(  firstname = fName,
                            lastName = lName,
                            email = uniqueName + '@test' + orgId + '.org',
                            Username = uniqueName + '@test' + orgId + '.org',
                            EmailEncodingKey = 'ISO-8859-1',
                            Alias = uniqueName.substring(18, 23),
                            TimeZoneSidKey = 'America/Los_Angeles',
                            LocaleSidKey = 'en_US',
                            LanguageLocaleKey = 'en_US',
                            ProfileId = profId,
                            UserRoleId = roleId);
    return tuser;
}

I had referred to some blog or community answer for this resolving issue way back. Don't have link of original post, but noticed that its now mentioned in Salesforce documentation here.

Answer 2

You can use System.now() as username with some prefix like

String username = 'Test'+string.valueOfGmt(System.now());