I can’t remember exactly when, but around the year 2000 my wife and I attended some training at the Fachhochschule in Kufstein, Austria, where we were both teaching. At the end, the group were asked for some ideas for future training days. At first, nobody said anything. Then, one of us suggested language testing. The general response can be encapsulated in one word: “why?”. It has been clear ever since that this part of our business is not given the importance it deserves, and I see no evidence that much has changed since then.
There is a frighteningly low level of knowledge in our business of language testing and much if not most of it is done with insufficient knowledge to be able to make reliable inferences about the results. There are of course exceptions to that statement, with some very knowledgeable people as well, and there is an IELTS SIG dedicated to this topic, but it is an area that needs strengthening. So, if you want to develop your knowledge in this area, the British Council is running a MOOC on this subject starting soon. It is led by two researchers in the Assessment Research Group at the Council, both of whom have extensive practical experience of teaching English as well as being highly knowledgeable about language testing. I took it last time and can confirm it is a very useful course for language teachers.
You can register here and you will be notified when it is starting: