My wife tested positive for covid yesterday . do i need to have myself tested if i do not exhibit any symptoms of covid ? i do suffer with a malignant brain tumour

Probably no: So sorry about your wife. There is a general belief that people with cancer have more severe problems with the Covid 19 disease, but several studies (e.g. breast cancer) have not confirmed that cancer is an actual co-morbidity, like age or diabetes, etc. Unless you need test status information for your domestic or business situation/exposure of others, I don't believe that testing is needed.

Test and quarantine: Absolutely you should get a test. This will help you determine if and for how long you need to quarantine. If you had close, prolonged exposure, I would suggest you try and stay away from people if possible until your test results are available. Wear your mask even in your home to prevent transmission. Try to rest and try not to overdo things. Also, relax, try some meditation.