Der erste Fehler: INVALID_CROSS_REFERENCE_KEY, Zugewiesen ID: Inhaber darf nicht leer sein: [OwnerId]

Als die erste option, die Sie einfügen können test-Nutzer:

 @isTest
 private class test{

     static TestMethod void Test1_TestInsertWithValue() {
         Meeting_Master__c master=new Meeting_Master__c();
         Event event =new Event();
         Profile p=[SELECT Id From Profile WHERE Name='Standard User'];
         User u2 =new User( Alias = 'newUser1' ,
                            Email ='[email protected]',
                            EmailEncodingKey = 'UTF-8',
                            LastName = 'Testing',
                            LanguageLocaleKey='en_US',
                            LocaleSidKey='en_US', //changed for to avoid: INVALID_OR_NULL_FOR_RESTRICTED_PICKLIST, Locale: bad value for restricted picklist field: America/Los_Angeles
                            UserName='[email protected]',
                            ProfileId=p.Id,
                            TimeZoneSidKey    = 'America/Los_Angeles');
         insert u2;

         event.OwnerId = u2.Id;
         event.StartDateTime = datetime.newInstance(2008, 12, 1);
         event.EndDateTime = datetime.newInstance(2008,12,10); //changed to 10-12-2008 for to avoid: FIELD_INTEGRITY_EXCEPTION, Event duration can not be longer than 14 days
         event.subject='call';
         event.WhatId=master.Id;
         Insert master;
         insert event;
     }

 }

Die zweite option ist zu versuchen zu verwenden System.runAs()
http://www.salesforce.com/us/developer/docs/apexcode/Content/apex_testing_tools_runas.htm

 @isTest
 private class test{

     static TestMethod void Test1_TestInsertWithValue() {
         Meeting_Master__c master=new Meeting_Master__c();
         Event event =new Event();
         Profile p=[SELECT Id From Profile WHERE Name='Standard User'];
         User u2 =new User( Alias = 'newUser1' ,
                            Email ='[email protected]',
                            EmailEncodingKey = 'UTF-8',
                            LastName = 'Testing',
                            LanguageLocaleKey='en_US',
                            LocaleSidKey='en_US', 
                            UserName='[email protected]',
                            ProfileId=p.Id,
                            TimeZoneSidKey    = 'America/Los_Angeles');

         Insert master;

         System.runAs(u2) {
            event.StartDateTime = datetime.newInstance(2008, 12, 1);
            event.EndDateTime = datetime.newInstance(2008,12,10);
            event.subject='call';
            event.WhatId=master.Id;

            insert event;
         }
     }

 }