Validate JSON values with Swagger Schema.

This module provides helpful functions for JSON validation. These functions are meant to be used in test suites for your application to ensure that JSON respresentation for your data corresponds to schemas you're using for the Swagger specification.

It is recommended to use validation functions as QuickCheck properties (see http://hackage.haskell.org/package/QuickCheck).

>>> validateToJSON "hello"
[]

>>> validateToJSON False
[]

>>> newtype Nat = Nat Integer deriving Generic
>>> instance ToJSON Nat where toJSON (Nat n) = toJSON n
>>> instance ToSchema Nat where declareNamedSchema proxy = genericDeclareNamedSchema defaultSchemaOptions proxy & mapped.minimum_ ?~ 0
>>> validateToJSON (Nat 10)
[]
>>> validateToJSON (Nat (-5))
["value -5.0 falls below minimum (should be >=0.0)"]

Because Maybe a has the same schema as a, validation generally fails for null JSON:

>>> validateToJSON (Nothing :: Maybe String)
["expected JSON value of type SwaggerString"]
>>> validateToJSON ([Just "hello", Nothing] :: [Maybe String])
["expected JSON value of type SwaggerString"]
>>> validateToJSON (123, Nothing :: Maybe String)
["expected JSON value of type SwaggerString"]

However, when Maybe a is a type of a record field, validation takes required property of the Schema into account:

>>> data Person = Person { name :: String, age :: Maybe Int } deriving Generic
>>> instance ToJSON Person
>>> instance ToSchema Person
>>> validateToJSON (Person "Nick" (Just 24))
[]
>>> validateToJSON (Person "Nick" Nothing)
[]