标签：#jest

Shifting from traditional application testing to serverless TypeScript engineering is all about shifting your perspective: you stop testing a running server, and you start testing how your function responds to events and SDK states. Here is a simple, practical example for each testing, using modern AWS SDK v3 syntax. 1. Unit Testing: Jest + Mock Payloads & SDK Client Mocking In unit tests, you don't call real AWS services. You pass a simulated API Gateway event to your handler, and you mock the AWS SDK so it returns predictable data instead of hitting live infrastructure. The Code Under Test ( src/handler.ts ) import { APIGatewayProxyEvent , APIGatewayProxyResult } from ' aws-lambda ' ; import { DynamoDBClient } from ' @aws-sdk/client-dynamodb ' ; import { DynamoDBDocumentClient , GetCommand } from ' @aws-sdk/lib-dynamodb ' ; const ddbClient = new DynamoDBClient ({}); const docClient = DynamoDBDocumentClient . from ( ddbClient ); export const handler = async ( event : APIGatewayProxyEvent ): Promise < APIGatewayProxyResult > => { const userId = event . pathParameters ?. id ; if ( ! userId ) { return { statusCode : 400 , body : JSON . stringify ({ message : ' Missing ID ' }) }; } // Fetch from DynamoDB const result = await docClient . send ( new GetCommand ({ TableName : process . env . USERS_TABLE , Key : { id : userId } })); if ( ! result . Item ) { return { statusCode : 404 , body : JSON . stringify ({ message : ' User not found ' }) }; } return { statusCode : 200 , body : JSON . stringify ( result . Item ), }; }; The Jest Unit Test ( tests/unit.test.ts ) Instead of the legacy aws-sdk-mock , the modern standard for AWS SDK v3 is aws-sdk-client-mock . import { handler } from ' ../src/handler ' ; import { APIGatewayProxyEvent } from ' aws-lambda ' ; import { mockClient } from ' aws-sdk-client-mock ' ; import { DynamoDBDocumentClient , GetCommand } from ' @aws-sdk/lib-dynamodb ' ; const ddbMock = mockClient ( DynamoDBDocumentClient ); describe ( ' Lambda Handler Unit

After months of using Jest for unit testing, we decided to take the plunge and migrate to the built-in node:test runner. The results were surprising, with some features working seamlessly and others requiring significant rework. In this post, we'll share our journey and the lessons we learned along the way. Introduction to node:test The node:test runner is a built-in testing framework that comes with Node.js. It's designed to be fast, efficient, and easy to use. Here's an example of a simple test using node:test: import { test } from ' node:test ' ; import { Command } from ' @aws-sdk/client-lambda ' ; test ( ' Lambda client test ' , async ( t ) => { const lambdaClient = new Command (); const response = await lambdaClient (); t . equal . responseStatusCode , 200 ; }); Warning: When using node:test, make sure to handle errors properly, as unhandled errors can cause the test runner to crash. Migrating from Jest to node:test Migrating from Jest to node:test requires some changes to your test code. One of the main differences is the way you handle ES modules. In Jest, you can use the jest.config.js file to configure how ES modules are handled. In node:test, you need to use the --test-type option to specify the type of test you're running. Here's an example of how to migrate a Jest test to node:test: // jest.test.js import { lambdaClient } from ' ../lambdaClient ' ; describe ( ' Lambda client test ' , () => { it ( ' should return 200 ' , async () => { const response = await lambdaClient (); expect ( response . statusCode ). toBe ( 200 ); }); }); // node-test.test.js import { test } from ' node:test ' ; import { lambdaClient } from ' ../lambdaClient ' ; test ( ' Lambda client test ' , async ( t ) => { const response = await lambdaClient (); t . equal ( response . statusCode , 200 ); }); Tip: Use the --coverage option to generate code coverage reports for your tests. Overcoming Incompatibilities and Limitations One of the main limitations of node:test is that it does not su