You're seeing just the macro refute_pipeline_receive, go back to Membrane.Testing.Assertions module for more information.
Link to this macro

refute_pipeline_receive(pipeline, message_pattern, timeout \\ 2000)

View Source (macro)

Asserts that pipeline has not received and will not receive a message from another process matching message_pattern within the timeout period specified in milliseconds.

The message_pattern must be a match pattern.

refute_pipeline_receive(pid, :tick)

Such call would flunk if the message :tick has been handled by c:Membrane.Parent.handle_other/3.