colcon can not find my package

I have been writing some ROS2 code in C++ using colcon on Ubuntu 20.04, all has been working fine, up until now. colcon all of a sudden started complaining that it couldn't find my packages. When I run colcon build --packages-select test I get the following error

WARNING:colcon.colcon_core.package_selection:ignoring unknown package 'test' in --packages-select

My test package is still in the ~ros/dev_ws/src directory. If I create a new package (test2 say), I can build it without error. Any help would be greatly appreciated