Azure Penetration Testing

Our firm has PaaS and IaaS resources deployed on Azure. We're undergoing a security audit by a prospective client who has asked how often Microsoft's security team conducts penetration tests of Azure systems and when the last test was performed. I have found various postings and white papers by Microsoft mentioning the internal penetration testing (https://technet.microsoft.com/en-us/security/mt346049.aspx, https://gallery.technet.microsoft.com/Cloud-Red-Teaming-b837392e), but none that give specifics that would allow us to answer the audit team's questions. Where could we find answers to these questions?

Thanks.