@isTest
private class TestRejectDoubleBooking{
static testmethod void TestDoubleBooking() {
    Datetime now = System.now();

    Speaker__c speaker = new Speaker__c(First_Name__c='John', Last_Name__c='Smith');
    insert speaker;

    Session__c session1 = new Session__c(Name='Session 1', Session_Date__c=now);
    insert session1;
    Session__c session2 = new Session__c(Name='Session 2', Session_Date__c=now);
    insert session2;

    Session_Speaker__c assignment1 =
    new Session_Speaker__c(Session__c=session1.Id, Speaker__c=speaker.Id);
    insert assignment1;

    Session_Speaker__c assignment2 =
    new Session_Speaker__c(Session__c=session2.Id, Speaker__c=speaker.Id);
    Database.SaveResult result = Database.insert(assignment2, false);
    
    System.assert(!result.isSuccess());
}


}