There is not any way to automate captcha submission. Actually, that's the reason captcha is used for. All you can do are:
ReCAPTCHA's documentation provides a set of keys that you can use for testing. You can also whitelist your testing domains for exclusion.
Run your tests on a development or staging environment and disable the CAPTCHA in that environment.
DesignIn your test in a way so that it submits, submit the form without submitting the captchaCAPTCHA and then checkscheck for the captchaCAPTCHA error. YouExpectedly you won't be able to successfully submit the form this way, but you'll be able to test whether it's validating properly or not.