jest-json-schema

JSON schema matcher for jest

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Matchers included

toMatchSchema(schema)

Validates that an object matches the given JSON schema

it('validates my json', () => {
  const schema = {
    properties: {
      hello: { type: 'string' },
    },
    required: ['hello'],
  };
  expect({ hello: 'world' }).toMatchSchema(schema);
});

Installation

$ npm install --save-dev jest-json-schema

Usage

In any test file:

import { matchers } from 'jest-json-schema';
expect.extend(matchers);

Or if you want it available for all test files then set it up the same way in a test framework script file

You can pass Ajv options using matchersWithOptions and passing it your options object. The only option passed by default is allErrors: true.

import { matchersWithOptions } from 'jest-json-schema';

const formats = {
  bcp47: /^[a-z]{2}-[A-Z]{2}$/,
}

expect.extend(matchersWithOptions({ formats }));

Additionally you can also use a callback to further configure and extend the Ajv instance used by the matchers:

import ajvKeywords from 'ajv-keywords';
import { matchersWithOptions } from 'jest-json-schema';

const formats = {
  bcp47: /^[a-z]{2}-[A-Z]{2}$/,
}

expect.extend(matchersWithOptions({ formats }, (ajv) => {
  // This uses the `ajv-keywords` library to add pre-made
  // custom keywords to the Ajv instance.
  ajvKeywords(ajv, ['typeof', 'instanceof']);
}));

You can also customize the Ajv class with the AjvClass option:

import Ajv2020 from 'ajv/dist/2020'
import { matchersWithOptions } from 'jest-json-schema';

expect.extend(matchersWithOptions({ AjvClass: Ajv2020 }));

Verbose errors

Ajv supports a verbose option flag which enables more information about individual errors. This extra information can mean that we can output to Jest more meaningful errors that can help the development process:

const { matchersWithOptions } = require('jest-json-schema');

expect.extend(matchersWithOptions({
  verbose: true
}));

test('check that property errors are outputted', () => {
  const schema = {
    $id: 'testSchema',
    type: 'object',
    properties: {
      name: {
        type: 'string',
      },
      dob: {
        type: 'string',
        format: 'date',
      },
    },
  };

  const invalidData = {
    name: null,
    dob: '02-29-2000',
  };

  expect(() => {
    expect(invalidData).toMatchSchema(schema)
  }).toThrowErrorMatchingInlineSnapshot(`
"expect(received).toMatchSchema(schema)

Received:
  .name should be string
    Received: <null>
    Path: testSchema#/properties/name/type
  .dob should match format \\"date\\"
    Received: <string> 02-29-2000
    Path: testSchema#/properties/dob/format
"
`);
});

Example using multiple schema files

If you organise your schemas into separate files and use refs which point to the various different schemas, it will be important to include those dependent schema files when extending Jest's expect handler, using the matchersWithOptions interface:

schemaA.json

{
  "$id": "schemaA",
  "$schema": "http://json-schema.org/draft-07/schema#",
  "description": "Example of a definition schema.",
  "definitions": {
    "testA": {
      "type": "number",
      "const": 1
    },
    "testB": {
      "type": ["null", "string"]
    }
  }
}

schemaB.json

{
  "$id": "schemaB",
  "$schema": "http://json-schema.org/draft-07/schema#",
  "description": "Example of a schema that references another schema.",
  "$ref": "schemaA#/definitions/testB"
}

schemaA.test.js

const { matchersWithOptions } = require('jest-json-schema');

// Local schema files are imported like normal. If you use TypeScript you
// will need to ensure `--resolveJsonModule` is enabled.
const schemaA = require('./schemaA.json');
const schemaB = require('./schemaB.json');

expect.extend(matchersWithOptions({
  // Loading in a schema which is comprised only of definitions,
  // which means specific test schemas need to be created.
  // This is good for testing specific conditions for definition schemas.
  schemas: [schemaA]
});

test('schemaA is valid', () => {
  expect(schemaA).toBeValidSchema();
});

test('using schemaA to build a test schema to test a specific definition', () => {
  // This is a test schema which references a definition in one of the
  // pre-loaded schemas. This can allow us to write tests for specific
  // definitions.
  const testSchema = {
    $ref: 'schemaA#/definitions/testA'
  };

  expect(testSchema).toBeValidSchema();

  // Valid
  expect(1).toMatchSchema(testSchema);

  // This example runs through a number of values that we know don't match
  // the schema, ensuring that any future changes to the schema will require
  // the test to be updated.
  ['1', true, false, null, [], {}].forEach(value => {
     expect(value).not.toMatchSchema(testSchema);
  });
});

test('using schemaB which already references a definition in schemaA', () => {
  expect(schemaB).toBeValidSchema();

  // Valid
  ['', '1', null].forEach(value => {
    expect(value).toMatchSchema(schemaB);
  });

  // Invalid
  ['1', true, false, [], {}].forEach(value => {
     expect(value).not.toMatchSchema(schemaB);
  });
});

TypeScript support

If you would like to use jest-json-schema library in your TypeScript project, remember to install type definitions from @types/jest-json-schema package.

npm install --save-dev @types/jest-json-schema

Or if yarn is your package manager of choice:

yarn add @types/jest-json-schema --dev

Contributing

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Please feel free to open pull requests and see CONTRIBUTING.md to learn how to get started contributing.

License

Any contributions made under this project will be governed by the Apache License 2.0.

Code of Conduct

This project adheres to the American Express Community Guidelines. By participating, you are expected to honor these guidelines.