cdk-testing

CDK Testing

Overview

Test CDK stacks and constructs with aws-cdk-lib/assertions. Use Template.fromStack() to inspect synthesized CloudFormation and assert on resources. Use snapshot tests for regression safety.

Dependencies

pnpm add -D aws-cdk-lib vitest

Template Assertions

// cdk/lib/stacks/api-stack.test.ts

import { describe, it, expect } from "vitest";
import { App } from "aws-cdk-lib";
import { Template } from "aws-cdk-lib/assertions";
import { ApiStack } from "./api-stack";

describe("ApiStack", () => {
  it("should create a REST API and Lambda functions", () => {
    const app = new App();
    const stack = new ApiStack(app, "TestStack", {
      dataTable: createMockTable(),
      idempotencyTable: createMockTable(),
      databaseSecret: createMockSecret(),
      rdsProxyEndpoint: "proxy.example.com",
      opensearchEndpoint: "https://search.example.com",
    });

    const template = Template.fromStack(stack);

    template.resourceCountIs("AWS::ApiGateway::RestApi", 1);
    template.resourceCountIs("AWS::Lambda::Function", 3);

    template.hasResourceProperties("AWS::Lambda::Function", {
      Runtime: "nodejs22.x",
      Handler: "index.handler",
      MemorySize: 512,
      Timeout: 30,
    });

    template.hasResourceProperties("AWS::Lambda::Function", {
      Environment: {
        Variables: expect.objectContaining({
          DYNAMODB_TABLE_NAME: expect.any(String),
        }),
      },
    });
  });
});

function createMockTable() {
  return {} as any; // Use actual Table from a test stack or @aws-cdk-lib/aws-dynamodb
}
function createMockSecret() {
  return {} as any;
}

Fine-Grained Assertions

const template = Template.fromStack(stack);

// At least one Lambda with these properties
template.hasResourceProperties("AWS::Lambda::Function", {
  Runtime: "nodejs22.x",
  Architectures: ["arm64"],
});

// SQS event source with reportBatchItemFailures
template.hasResourceProperties("AWS::Lambda::EventSourceMapping", {
  EventSourceArn: expect.any(String),
  FunctionName: expect.any(String),
  BatchSize: 10,
});

// DynamoDB table with TTL
template.hasResourceProperties("AWS::DynamoDB::Table", {
  BillingMode: "PAY_PER_REQUEST",
  StreamSpecification: { StreamViewType: "NEW_AND_OLD_IMAGES" },
});