You will be able to create an AdWords test account to experiment with the AdWords API and test out the dummy data. You may refer to the steps mentioned in
this guide on how to start the API signup process and make the API call. You can create an AdWords Manager account directly through
this link. Once the test manager account is created, you will be able to
setup the OAuth2 credentials to make API calls. With these test accounts, you will be able to experiment the API and make API calls but you will not be able to serve any ads. You may refer to
this guide which explains in detail on how test accounts work and
this guide on how to start developing with test accounts. Let me know if you have any other questions.