You’ll get an error about a non-validated input variable. You might get the following errors:

WARNING | Detected access of super global var $_POST,probably need manual inspection.

ERROR | Detected usage of a non-validated input variable: $_POST

WPCS is asking you to validate that the auth_step key even exists in the $_POST array.To fix that error, you’d modify your code to look like this:

if ( isset( $_POST['auth_step'] ) && 'test_value' === $_POST['auth_step'] ) ) { // ...

In addition to isset() you could also use empty() to validate the data. That allows you to check that the value is sent and isn’t empty at the same time: