integ-tests: broken assertion caused by getAttX calls

[nmussy]

Describe the bug

Running getAtt or getAttString on a SDK integration will cause the flattenResults property to be set, allowing users to retrieve JSONPath-ish property values. However, this also causes assertions for that integration to fail

Expected Behavior

Given that flattenResults is not exposed to the user, they would expect their object/path assertions to work regardless of getAttX calls.

Current Behavior

actual is undefined:

aws-cdk/packages/@aws-cdk/integ-tests-alpha/lib/assertions/providers/lambda-handler/assertion.ts

Line 9 in 8f4d4d7

let actual = decodeCall(request.actual);

Reproduction Steps

import * as cdk from 'aws-cdk-lib';
import { ExpectedResult, IntegTest } from '../../../lib';

const app = new cdk.App();

const stack = new cdk.Stack(app, 'foo');

const integ = new IntegTest(app, 'Integ', {
  testCases: [stack],
});

const models = integ.assertions.awsApiCall('Bedrock', 'GetFoundationModel', {
  modelIdentifier: 'amazon.titan-embed-text-v1',
});

models.expect(ExpectedResult.objectLike({
  modelDetails: { modelId: 'amazon.titan-embed-text-v1' },
}));

// Enabling this line will cause the assertion to fail
// eslint-disable-next-line no-console
// console.log(models.getAttString('modelDetails.modelName'));

Output:

Expected type object but received undefined

Possible Solution

I'm assuming the flattened object is not being sent/parsed properly. Reversion the flattening process in AssertionHandler would be satisfactory

Additional Information/Context

No response

CDK CLI Version

2.144.0

Framework Version

No response

Node.js Version

v20.11.1

OS

macOS 14.4.1

Language

TypeScript

Language Version

No response

Other information

I discovered this issue while attempting to write an integration test for #30361, which implements flattenResults for HTTP assertions