You can write tests for the Grape APIs using Rack or Rails, which should help you verify that the result is what you expected.
https://github.com/intridea/grape#writing-tests
I'm not sure it works with Sinatra / Grape, but you can also add Simplecov to make sure you have covered your base.
If you have already written tests and still have a problem, can you provide more information about the error you are getting?
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