Testing: assert a message is not sent

Starting to learn creating nodes and testing them using the node-red-test-helper module. (coming from python)

I have a node with multiple outputs. Based on a certain input I want to test whether certain outputs are sending out data (ie. on payload input==1, output1 should be true, output2 should be false).

I know how to test output (using the helper node and calling the done function). But I don't know how to test an output is NOT getting data.

Any help appreciated !