Help! - I can't even run the example

So, this is embarrasing.  I am new to PowerBI and want to setup a custom visual. I can't even run the 'update count' example which is provided as the defaut code for a new custom visual.

After is setup the new project:

pbiviz new test

Enable developer tools etc in PowerBI.  And insert the visual.  The visual shows Update Count 0. The Console shows the 'Visual Constructor' line.

When I change the figure, the update count does not change. The console also does not show the 'Visual update' output.  I am not sure that 'update' has even been called.

Have I broken somthing?   How do I get it to work?

Thanks in advance.

Mark