Testing your resolver and function handlers in AWS AppSync

You can use the EvaluateCode API command to remotely test your resolver and function handlers with mocked data before ever saving your code to a resolver or function. To get started with the command, make sure you have added the appsync:evaluatecode permission to your policy. For example:

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Action": "appsync:evaluateCode",
            "Resource": "arn:aws:appsync:<region>:<account>:*"
        }
    ]
}

You can leverage the command by using the AWS CLI or AWS SDKs. For example, to test your code using the CLI, simply point to your file, provide a context, and specify the handler you want to evaluate:

aws appsync evaluate-code \
  --code file://code.js \
  --function request \
  --context file://context.json \
  --runtime name=APPSYNC_JS,runtimeVersion=1.0.0

The response contains an evaluationResult containing the payload returned by your handler. It also contains a logs object that holds the list of logs that were generated by your handler during the evaluation. This makes it easy to debug your code execution and see information about your evaluation to help troubleshoot. For example:

{
    "evaluationResult": "{\"operation\":\"PutItem\",\"key\":{\"id\":{\"S\":\"record-id\"}},\"attributeValues\":{\"owner\":{\"S\":\"John doe\"},\"expectedVersion\":{\"N\":2},\"authorId\":{\"S\":\"Sammy Davis\"}}}",
    "logs": [
        "INFO - code.js:5:3: \"current id\" \"record-id\"",
        "INFO - code.js:9:3: \"request evaluated\""
    ]
}

The evaluation result can be parsed as JSON, which gives:

{
  "operation": "PutItem",
  "key": {
    "id": {
      "S": "record-id"
    }
  },
  "attributeValues": {
    "owner": {
      "S": "John doe"
    },
    "expectedVersion": {
      "N": 2
    },
    "authorId": {
      "S": "Sammy Davis"
    }
  }
}

Using the SDK, you can easily incorporate tests from your test suite to validate your code's behavior. Our example here uses the Jest Testing Framework, but any testing suite works. The following snippet shows a hypothetical validation run. Note that we expect the evaluation response to be valid JSON, so we use JSON.parse to retrieve JSON from the string response:

const AWS = require('aws-sdk')
const fs = require('fs')
const client = new AWS.AppSync({ region: 'us-east-2' })
const runtime = {name:'APPSYNC_JS',runtimeVersion:'1.0.0')

test('request correctly calls DynamoDB', async () => {
  const code = fs.readFileSync('./code.js', 'utf8')
  const context = fs.readFileSync('./context.json', 'utf8')
  const contextJSON = JSON.parse(context)
  
  const response = await client.evaluateCode({ code, context, runtime, function: 'request' }).promise()
  const result = JSON.parse(response.evaluationResult)
  
  expect(result.key.id.S).toBeDefined()
  expect(result.attributeValues.firstname.S).toEqual(contextJSON.arguments.firstname)
})

This yields the following result:

Ran all test suites.
> jest

PASS ./index.test.js
✓ request correctly calls DynamoDB (543 ms)
Test Suites: 1 passed, 1 total
Tests: 1 passed, 1 total
Snapshots: 0 totalTime: 1.511 s, estimated 2 s