Yes. When you fill out an application for admission, you must self-report your required test results in the Test Scores section of the application. However, you may also input any future test dates as well. If you have not taken a required test yet, inputting a future test date will allow you to submit the application.
If you have not yet taken a test that is required, you should register for the test as soon as possible and enter your future test date on the application. Be sure that your official scores are sent to Yale Graduate School of Arts and Sciences (see Required Examinations) and your scores will match with your application when they arrive. You should take any required testing as soon as possible to ensure ample time for your official scores to arrive, but you do not need to have test results in hand in order to submit your application.