CDK

This section shows how you can use sls-jest with the CDK.

When writing tests, you often need to access your deployed resources. It can be the name of a DynamoDB table, an API Gateway endpoint url, the ARN of a Step Function state machine, etc.

When those values are predictable, it is usually not an issue, but this is not always the case. e.g. ARNs are not always predictable, or if you let CloudFormation name your resources with a random name.

The CDK has an --outputs-file parameter which prints the stack outputs in a file. You can use that to export the values that you need, and access them from jest.

Example:

If you want to access a DynamoDB table name, you can do:

// myStack.ts
const myTable = new Table(this, 'MyTable', {
  partitionKey: { name: 'pk', type: AttributeType.STRING },
  sortKey: { name: 'sk', type: AttributeType.STRING },
  billingMode: BillingMode.PAY_PER_REQUEST,
});

new CfnOutput(this, 'MyTableName', {
  value: myTable.tableName,
});

Deploy:

cdk deploy --all --outputs-file .sls-jest/resources.json

Which genereates a file looking like this:

// .sls-jest/resources.json
{
  "myStack": {
    "MyTableName": "myStack-MyTable72A94F83-WEE9G8164XWC"
  }
}

You can now access your resource from jest.

import { truncateTable } from 'sls-jest';
import resources from './.sls-jest/resources.json';

const myTable = resources.myStack.MyTableName;

beforeEach(async () => {
  await truncateTable(myTable);
});