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1.1.9 • Public • Published


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Unit test AppSync VTL resolvers, with popular frameworks such as Jest.



yarn add appsync-template-tester --dev
import Parser from 'appsync-template-tester';
import { readFileSync } from 'fs';
import { join } from 'path';

// Load from a file (if not in a string already)
const templateFilePath = join(__dirname, './pathToFile.vtl');
const template = readFileSync(templateFilePath, {
  encoding: 'utf8',

// Create the resolver
const parser = new Parser(template);

test('Test the resolver', () => {
  // The Appsync Context (ctx) object
  const context = {
    // For example with a dynamoDB response resolver:
    result: {
      id: 'testId',
      // ...

  // parser.resolve() automatically typecasts (note JSON becomes a JS object for ease of testing)
  const response = parser.resolve(context);

  // For convenience, the response is returned as a JS object rather than JSON

Util helpers supported

This module supports all the provided core, map & time $util methods, and most of the dynamodb methods. The underlying methods can be seen in the Resolver Mapping Template Utility Reference docs.

Note: The errors list is also not returned (but $util.error will throw an error).

Built by Skyhook

This module is contributed by the team at Skyhook. And extended by SpecifAI for internal use of testing AppSync, but it should be useable for everyone using AppSync and wants to test the VTL templates. We switched from Amplify-appsync-simulator to this package because the simulator needs more setting up, which is to extensive for just unittesting. The package from Skyhook lacked some support see (https://github.com/skyhookadventure/appsync-template-tester/issues/17) and therefore we added support by merging code based on (https://github.com/aws-amplify/amplify-cli/tree/master/packages/amplify-appsync-simulator/src/velocity)

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npm i @specifai-net/appsync-template-tester

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  • jeroenmeulendijks