First of all, psychometric tests will fail the a couple of tests set forth by article 5 GDPR. It cannot be considered fair that a data subject's right to work (art. 15 Charter) is determined by a process which is based on pseudoscience. It'll also fail the necessity test because it is simply not necessary to use such intrusive tests in your recruitment process.

Psychometric testing is based on pseudoscience and from an ethical perspective it disgusts me that you are even using(or wanting to use) psychometric tests.

Second of all, you cannot get valid consent from an (prospective) employee because there's a clear imbalance of power, and any consent given is thus not freely given.

You will not be able to rely on any other legal ground for processing because psychometric tests are special categories of personal data (health data). Some people will argue that psychometric tests are not health data, but the scope of health data is very broad, it also encompasses data about a data subject's intellectual and emotional capacity. This has also been previously confirmed by the WP29.

Because the processing of psychometric testing falls under Art. 9 GDPR you can only process it with consent or if one of the exemptions apply. And we already established that you cannot obtain valid consent, and there's no exemptions that apply insofar I'm aware under member state law.

In conclusion, there is no way to obtain valid consent for psychometric testing, nor is there any other lawful basis to use psychometric testing as part of your recruitment process. Moreover, the use of such testing will fail the requirements of art. 5 GDPR regarding fairness and necessity test, which are also general principles of EU law.