With Moldable Development we use examples rather than tests. Basically these are unit tests that return a live instance that you can interact with.
In this case having an example (test) without assertions is useful to start the live programming flow. The test (example) with assertions (re)uses the bare example that is the basis for live programming. The test with assertions can't be used for live programming if it fails.
The idea was elaborated by Dr. Markus Gälli in his PhD thesis "Modeling Examples to Test and
Understand Software" pdf 
in 2006, and it turns out to be enormously valuable in practice. post
~
Oscar Nierstrasz linkedin comments on Kent Beck's post:
Write a list of the test scenarios you want to cover …