Using HR departments to give tests over the phone is only usefull if the tests are multiple choice, as otherwise they have to interpret your answers if they don't match exactly the answers that the tech people give them.

But in general I've found that tech tests are hit and miss when it comes to getting the job. I've had tests, such as on C, where I've got fewer than half the questions right and got the job. At the other extreme I've got 23/25 and not got the job!