With earlier elm versions, a separate package file is maintained for
tests, which when properly configured enabled the compiler to find what
it needed to compile the tests. Under elm 0.19, test dependencies are
managed in the top-level package file, so `elm make` will fail on the
tests. `elm-test make` is required in this case.
See https://github.com/elm-explorations/test/issues/64
Aryeh Leib Taurog