Run As Partner Portal User or Partner Community User in Apex Test Class

There are some scenarios where we need to do unit testing as a Partner Portal/Partner Community user. Below code can be used to create partner portal user and run the logic as that user.

Syntax:

@isTest
private class testClass{
    public static testMethod void testFunction(){               
        //Create account
        Account portalAccount1 = new Account(
            Name = 'TestAccount'
        );
        Database.insert(portalAccount1);
     
        //Create contact for the account, which will enable partner portal for account
        Contact contact1 = new Contact(
            FirstName = 'Test',
            Lastname = 'Amit',
            AccountId = portalAccount1.Id,
            Email = 'test@test.com'
        );
        Database.insert(contact1);
       
        //Create user for the contact
        Profile portalProfile = [SELECT Id FROM Profile WHERE Name = 'Gold Partner User' Limit 1];
        User user1 = new User(
            Username = 'test12345test@test.com',
            ContactId = contact1.Id,
            ProfileId = portalProfile.Id,
            Alias = 'test123',
            Email = 'test12345@test.com',
            EmailEncodingKey = 'UTF-8',
            LastName = 'Kumar',
            CommunityNickname = 'test12345',
            TimeZoneSidKey = 'America/Los_Angeles',
            LocaleSidKey = 'en_US',
            LanguageLocaleKey = 'en_US'
        );
        Database.insert(user1);
       
        system.runAs(user1){
            Account a = new Account(name='test'); 
            insert(a); 
        }                               
    }
}

Note:

1. Owner of the user should have a role. so make sure your admin user has a role or you can create one admin user in the test class with appropriate role.
2. Make sure partner portal / partner community is enable for your org and respective profile has the access of it.