@isTest
private class TestRunAs {
     public static testMethod void testRunAs() {
       // Setup test data
      // This code runs as the system user
       Profile p = [SELECT Id FROM Profile WHERE Name='Standard User'];
    User u = new User(Alias = 'standt', Email='standarduser@testorg.com',
        EmailEncodingKey='UTF-8', LastName='Testing', LanguageLocaleKey='en_US',
        LocaleSidKey='en_US', ProfileId = p.Id,
        TimeZoneSidKey='America/Los_Angeles', UserName='standarduser@testorg.com');

    System.runAs(u) {
         Opportunity opp = new Opportunity();
         // put required field
         insert opp;

         OpportunityTeamMember otm = new OpportunityTeamMember (OpportunityId = opp.id,UserId = u.id,TeamMemberRole = role);
 insert otm;

    }
  }
}