Why not write tests inline with code?

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Chris Devereaux has recently been reading up on “Literate Programming,” an innovative (and mostly unused) approach to programming developed by Donald Knuth in the 1970s. It got him thinking about new ways of implementing tests. “Well-written tests, especially BDD-style specs, can do a better job of explaining what code does than prose does,” he writes in his question. Also, tests “have the big advantage of verifying their own accuracy.” Still, Chris has never seen tests written inline with the code they test. Why not?

See the original question here.