chore(cli): add integration test for Lambda function's hotswap feature

This commit adds a basic integration test for the hotswap feature, for
the case when the Lambda function's description and environment variables
have changed.

packages/aws-cdk/test/integ/cli/app/app.js

@@ -228,6 +228,24 @@ class LambdaStack extends cdk.Stack {
   }
 }
 
+class LambdaHotswapStack extends cdk.Stack {
+  constructor(parent, id, props) {
+    super(parent, id, props);
+
+    const fn = new lambda.Function(this, 'my-function', {
+      code: lambda.Code.asset(path.join(__dirname, 'lambda')),
+      runtime: lambda.Runtime.NODEJS_14_X,
+      handler: 'index.handler',
+      description: new Date().toISOString(),
+      environment: {
+        SomeVariable: new Date().toISOString(),
+      }
+    });
+
+    new cdk.CfnOutput(this, 'FunctionName', { value: fn.functionName });
+  }
+}
+
 class DockerStack extends cdk.Stack {
   constructor(parent, id, props) {
     super(parent, id, props);
@@ -379,6 +397,7 @@ switch (stackSet) {
     new MissingSSMParameterStack(app, `${stackPrefix}-missing-ssm-parameter`, { env: defaultEnv });
 
     new LambdaStack(app, `${stackPrefix}-lambda`);
+    new LambdaHotswapStack(app, `${stackPrefix}-lambda-hotswap`);
     new DockerStack(app, `${stackPrefix}-docker`);
     new DockerStackWithCustomFile(app, `${stackPrefix}-docker-with-custom-file`);
     new FailedStack(app, `${stackPrefix}-failed`)

packages/aws-cdk/test/integ/cli/cli.integtest.ts

@@ -1096,6 +1096,32 @@ integTest('test resource import', withDefaultFixture(async (fixture) => {
   }
 }));
 
+integTest('hotswap deployment supports Lambda function\'s description and environment variables', withDefaultFixture(async (fixture) => {
+  // GIVEN
+  const stackArn = await fixture.cdkDeploy('lambda-hotswap', {
+    captureStderr: false,
+  });
+
+  // WHEN
+  const deployOutput = await fixture.cdkDeploy('lambda-hotswap', {
+    options: ['--hotswap'],
+    captureStderr: true,
+    onlyStderr: true,
+  });
+
+  const response = await fixture.aws.cloudFormation('describeStacks', {
+    StackName: stackArn,
+  });
+  const functionName = response.Stacks?.[0].Outputs?.[0].OutputValue;
+
+  // THEN
+
+  // The deployment should not trigger a full deployment, thus the stack's status must remains
+  // "CREATE_COMPLETE"
+  expect(response.Stacks?.[0].StackStatus).toEqual('CREATE_COMPLETE');
+  expect(deployOutput).toContain(`Lambda Function '${functionName}' hotswapped!`);
+}));
+
 async function listChildren(parent: string, pred: (x: string) => Promise<boolean>) {
   const ret = new Array<string>();
   for (const child of await fs.readdir(parent, { encoding: 'utf-8' })) {