Magic of Merging Columns

Try this simple change in your Kanban Board.
Merge “Development” & “Testing” columns in a single column and call it “Building”.
Needless to say, any work-item will pass this "Building" column only after a joint concurrence by Dev & QA.

To implement this, maybe you will face some reluctance.
Maybe they will say "why to change when it is working fine".
Maybe you will face vehement resistance.
Maybe they will say "this is not the way it works here".

If they tell you any of the above, it is a sign of they are striving for local optima. 
But if you manage to change it, just in a matter of few days you will see the power of visualizing TCs in advance.
You will see a reduction in ping-pong between Dev & QC.
You will see the magic of parallel testing.
You will see the boost in quality just in a matter of a few days.