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Verify that every type used with JSON content type in a servant API has compatible ToJSON and ToSchema instances using validateToJSON.

validateEveryToJSON will produce one prop specification for every type in the API. Each type only gets one test, even if it occurs multiple times in the API.

>>> data User = User { name :: String, age :: Maybe Int } deriving (Show, Generic, Typeable)
>>> newtype UserId = UserId String deriving (Show, Generic, Typeable, ToJSON, Arbitrary)
>>> instance ToJSON User
>>> instance ToSchema User
>>> instance ToSchema UserId
>>> instance Arbitrary User where arbitrary = User <$> arbitrary <*> arbitrary
>>> type UserAPI = (Capture "user_id" UserId :> Get '[JSON] User) :<|> (ReqBody '[JSON] User :> Post '[JSON] UserId)

>>> hspec $ context "ToJSON matches ToSchema" $ validateEveryToJSON (Proxy :: Proxy UserAPI)

ToJSON matches ToSchema
  User
  UserId

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2 examples, 0 failures

For the test to compile all body types should have the following instances:

• ToJSON and ToSchema are used to perform the validation;
• Typeable is used to name the test for each type;
• Show is used to display value for which ToJSON does not satisfy ToSchema.
• Arbitrary is used to arbitrarily generate values.

If any of the instances is missing, you'll get a descriptive type error:

>>> data Contact = Contact { fullname :: String, phone :: Integer } deriving (Show, Generic)
>>> instance ToJSON Contact
>>> instance ToSchema Contact
>>> type ContactAPI = Get '[JSON] Contact
>>> hspec $ validateEveryToJSON (Proxy :: Proxy ContactAPI)
...
    No instance for (Arbitrary Contact)
      arising from a use of ‘validateEveryToJSON’
...