Yes, access to the test (OT&E) environment for API is possible once you are a registered Trademark Clearinghouse Agent.
After your account has been verified, you can request your OT&E credentials by raising a Support ticket on our dedicated Customer Support System. To do this, click on "GET SUPPORT" on the TMCH interface or send an email to support[at]trademark-clearinghouse[dot]com. You will receive your OT&E credentials and the necessary URLs to access both the OT&E web interface and the OT&E API interface.
Please refer to our detailed manual on how to use the OT&E environment.