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Hypothesis strategies for GraphQL schemas and queries

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Hypothesis strategies for GraphQL schemas, queries and data.

NOTE This package is experimental, some features are not supported yet.


There are a few strategies for different use cases.

  1. Schema generation - hypothesis_graphql.strategies.schemas()

  2. Query - hypothesis_graphql.strategies.queries(schema).

  3. Mutation - hypothesis_graphql.strategies.mutations(schema).

Lets take this schema as an example:

type Book {
  title: String
  author: Author

type Author {
  name: String
  books: [Book]

type Query {
  getBooks: [Book]
  getAuthors: [Author]

type Mutation {
  addBook(title: String!, author: String!): Book!
  addAuthor(name: String!): Author!

Then strategies might be used in this way:

from hypothesis import given
from hypothesis_graphql import strategies as gql_st

SCHEMA = "..."  # the one above

def test_query(query):
    # This query might be generated:
    # query {
    #   getBooks {
    #     title
    #   }
    # }

def test_mutation(mutation):
    # This mutation might be generated:
    # mutation {
    #   addBook(title: "H4Z\u7869", author: "\u00d2"){
    #     title
    #   }
    # }


To restrict the set of fields in generated operations use the fields argument:

@given(gql_st.queries(SCHEMA, fields=["getAuthors"]))
def test_query(query):
    # Only `getAuthors` will be generated

It is also possible to generate custom scalars. For example, Date:

from hypothesis import strategies as st, given
from hypothesis_graphql import strategies as gql_st, nodes

SCHEMA = """
scalar Date

type Query {
  getByDate(created: Date!): Int

            # Standard scalars work out of the box, for custom ones you need
            # to pass custom strategies that generate proper AST nodes
            "Date": st.dates().map(nodes.String)
def test_query(query):
    # Example:
    #  { getByDate(created: "2000-01-01") }

The hypothesis_graphql.nodes module includes a few helpers to generate various node types:

  • String -> graphql.StringValueNode

  • Float -> graphql.FloatValueNode

  • Int -> graphql.IntValueNode

  • Object -> graphql.ObjectValueNode

  • List -> graphql.ListValueNode

  • Boolean -> graphql.BooleanValueNode

  • Enum -> graphql.EnumValueNode

  • Null -> graphql.NullValueNode (a constant, not a function)

They exist because classes like graphql.StringValueNode can’t be directly used in map calls due to kwarg-only arguments.

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