Possibly pregnant

So today was my SO af due date, she swore up and down she was going to get her period, but She always gets cramping before her period not once did she complain this month of cramping or any of her usual period symptoms. So I had her take a test. Also how reliable is the clearblue advanced test? We are extremely excited as we have been ttc for about 5 months now but we dont want to get our hopes up if its possible these tests read false positives.