The bazel-built test executable was executing but not succeeding because the
validation code was not getting linked in at compile-time and the test used
lazy duck-typing to validate. This patch

1. makes the test fail loudly if an input doesn't implement the correct interface
2. updates the bazel rule to link in the validation code
3. fixes the test code so it imports the validation code
4. modifies the CI script to also run the tests via bazel