Articulating the ineffable. Programming language theory 
cognitive psychology. PhD @Stanford
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But I think there's important limitations to "let the computer trace for you". Sometimes you want to trace symbolically to answer questions like "will this pointer ever be null when it's derefed?"
And sometimes you want to trace in terms of a partially specified piece of data. Eg "if I had a database with 10 rows, would what would this function do?" And there's often more overhead to mocking a test that actually does this than mentally imagining it.
Nice looking prototype. Seems harder to retrofit this idea on existing languages. To work well perhaps the language and environment would have to be redesigned with this in mind. I imagine a system designed for abstract interpretation for values, types and "predicated types".
(aka refinement types?) Agree the cost of specifying the scenario needs to be very little. I imagine the abstract interpreter "fills in the blanks" lazily with values or types, on demand, and the UI allows you to further refine them (instead of specifying a complete testmock)
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