Can we test whether Lambda is connected with correct subnets using AWS CDK assertions, Jest during the runtime synth?

Question

I have a global stack, where I have my predefined VPCs and subnets

  export class GlobalStack extends InternalStack {
    /**
     * Shared VPC Instance
     */
    public readonly vpc = Vpc.fromLookup(this, 'vpc', {
      vpcId: process.env.VPC_ID!,
    })
  
    /**
     * Private Subnet 1 
     */
    public privateSubnet1 = new Subnet(this, 'subnet-1', {
      vpcId: this.vpc.vpcId,
      cidrBlock: 'xx.x.x.x/xx',
      availabilityZone: `${this.region}-1`,
    })
  
    /**
     * Private Subnet 2 
     */
    public privateSubnet2 = new Subnet(this, 'subnet-2', {
      vpcId: this.vpc.vpcId,
      cidrBlock: 'xx.x.x.x/xx',
      availabilityZone: `${this.region}-2`,
    })
  
    /**
     * Private Subnet 3 
     */
    public privateSubnet3 = new Subnet(this, 'subnet-3', {
      vpcId: this.vpc.vpcId,
      cidrBlock: 'xx.x.x.x/xx',
      availabilityZone: `${this.region}-3`,
    })

    public readonly apiGatewayVpcEndpoint = this.vpc.addInterfaceEndpoint(
        'ApiGateway',
        {
          service: InterfaceVpcEndpointAwsService.APIGATEWAY,
          subnets: {
            subnets: [
              this.privateSubnet1,
              this.privateSubnet2,
              this.privateSubnet3,
            ],
          },
        }
      )
}

And Once I get these vpc and subnet , I pass them to our lambda , which we have an enhanced node js lambda (a wrapper around node js lambda function), where I check if vpc props are available, I will add the defined three subnets.

The constructor of my lambda function:

constructor(scope: Construct, id: string, props: EnhancedNodeJsLambdaProps) {
    super(scope, id, {
      ...props,
      ...(props.vpc && {
        vpcSubnets: props.vpc.selectSubnets({
          subnetFilters: [
            SubnetFilter.containsIpAddresses(['xx.x.x.x/xx', 'xx.x.x.x/xx', 'xx.x.x.x/xx']
            ),
          ],
        }),
      }),
      runtime: props.runtime || Runtime.NODEJS_12_X,
      tracing: Tracing.ACTIVE,
    })
}

So now when I try to test my lambda, whether the subnets are attached to it, I either get some dummy az values or it returns that the lambda isn't connected with subnets, how can I test the same?

FYR, I will attach some of my test cases below

it('testing vpc subnets ', async () => {
    const app = new cdk.App()
    const topicsStack = new cdk.Stack(app, 'TopicsStack')
    const globalStack = await new GlobalStack(app, 'global-stack', {
      stackName: 'global-stack',
      description: 'Global Resources (Shared at the account level)',
      env: {
        account: '11111111',
        region: 'us-east-1',
      },
      envName: 'test',
    })
    let newLambda = new EnhancedNodeJsLambda(topicsStack, 'test-lambda', {
      entry,
      connectionReuseEnabled: true,
      vpc: globalStack.vpc,
    })

    console.log(
        globalStack.vpc.selectSubnets({
          subnetFilters: [
            SubnetFilter.containsIpAddresses(['xx.x.x.x/xx', 'xx.x.x.x/xx', 'xx.x.x.x/xx']),
          ],
        }).availabilityZones
      )
    //how to test subnets are properly linked?
  })

Also about the dummy values, the console log in the test case above returns me some dummy az values instead of my code ones:

the console log returns

[ 'dummy1a', 'dummy1b' ]

I tried to test the connection by adding the below code to the test case above

    const othertemp = Template.fromStack(topicsStack)
    othertemp.hasResourceProperties('AWS::Lambda::Function', {
      VpcConfig: {
        SubnetIds: globalStack.vpc.selectSubnets({
          subnetFilters: [
            SubnetFilter.containsIpAddresses(['xx.x.x.x/xx', 'xx.x.x.x/xx', 'xx.x.x.x/xx']
            ),
          ],
        }),
      },
    })

But it failed saying

    with the following mismatches:
        Expected type object but received array at /Properties/VpcConfig/SubnetIds (using objectLike matcher)

Also the subnet id's and az's are dummy values and not my intended ones.

I'm not sure why it's returning dummy values instead of my pre-defined one, and also I don't know how to test the lambda is connected with the correct subnets or no.

Answer 1

Well, not sure how to do it with CDK assertions, but I was able to get it done with jest assertions:

expect(myFunction.Properties.VpcConfig.SubnetIds).toEqual('my-subnet-ids');