IntegTest ExpectedResult : How to test for an empty array?

[jvalore-medallia]

Testing the response of a Lambda in an IntegTest, and if it returns some data, then assertAtPath works correctly like this:

  invoke.assertAtPath(
    'Payload.data.0.value',
    ExpectedResult.stringLikeRegexp('testvalue'),
  );

From the CloudWatch logs for the SingletonFunction, I get:

INFO	Event: 
{
    "RequestType": "Create",
    "ServiceToken": "arn:aws:lambda:...omitted...",
    "ResponseURL": "...",
    "StackId": "arn:aws:cloudformation:...omitted...",
    "RequestId": "...",
    "LogicalResourceId": "LambdaInvokec893c691437e1098611bc0301f404275",
    "ResourceType": "Custom::DeployAssert@SdkCallLambdainvoke",
    "ResourceProperties": {
        "ServiceToken": "arn:aws:lambda:...omitted...",
        "flattenResponse": "true",
        "salt": "...",
        "service": "Lambda",
        "expected": "{\"$StringLike\":\"testvalue\"}",
        "actualPath": "Payload.data.0.value",
        "api": "invoke",
        "parameters": { ...omitted... },
        "outputPaths": [
            "Payload.data.0.key",
            "Payload.data.0.value"
        ]
    }
}

The Lambda returns:

INFO	SDK response received 
{
    "ExecutedVersion": "$LATEST",
    "Payload": "{\"data\":[{\"env\":\"comdev\",\"instance\":\"comdev\",\"app\":\"test\",\"key\":\"testkey\",\"type\":\"SETTING\",\"value\":\"testvalue\"}]}",
    "StatusCode": 200
}

and the integ test runner forwards the paths

INFO	Returning result 
{
    "apiCallResponse.Payload.data.0.key": "testkey",
    "apiCallResponse.Payload.data.0.value": "testvalue"
}

That works well 🎉

---

However if My lambda was to return data: [] then I am struggling to figure out how to test that...
I tried:

  invoke.assertAtPath('Payload.data', ExpectedResult.arrayWith([]));

but that does not work. It seems like it doesn't even pull the data (empty array) off the path properly?

From the CloudWatch logs again:

INFO	Event: 
{
    "RequestType": "Create",
    "ServiceToken": "arn:aws:lambda:...",
    "ResponseURL": "...",
    "StackId": "arn:aws:cloudformation:...",
    "RequestId": "...",
    "LogicalResourceId": "LambdaInvoke...",
    "ResourceType": "Custom::DeployAssert@SdkCallLambdainvoke",
    "ResourceProperties": {
        "ServiceToken": "arn:aws:lambda:...",
        "flattenResponse": "true",
        "salt": "...",
        "service": "Lambda",
        "expected": "{\"$ArrayWith\":[]}",
        "actualPath": "Payload.data",
        "api": "invoke",
        "parameters": {...omitted...},
        "outputPaths": [
            "Payload.data"
        ]
    }
}

The outputPaths appears to be set correctly.
The Lambda returns:

INFO	SDK response received 
{
    "ExecutedVersion": "$LATEST",
    "Payload": "{\"data\":[]}",
    "StatusCode": 200
}

But [] is not plucked from Payload.data, instead it is ... undefined? non existant?

INFO	Returning result 
{}

INFO	Testing equality between undefined and "{\"$ArrayWith\":[]}"

and my test fails.
It seems like something should have been returned for that path, but 🤷

---

What is the correct way to test for an empty array? Or is this just a bug?

[jvalore-medallia]

Digging in to the behavior, it looks like the flatten method used to turn JSON objects into the "paths" structure just can't handle an empty array.

https://github.com/aws/aws-cdk/blob/main/packages/@aws-cdk/sdk-v2-to-v3-adapter/lib/api-call.ts#L157-L172

I added a unit test for it

test('can handle empty arrays', () => {
  expect(flatten({
    a: { b: 'c' },
    d: [
    ],
    e: ['f', 'g'],
  })).toEqual({
    'a.b': 'c',
    'd': [],
    'e.0': 'f',
    'e.1': 'g',
  });
});

which then fails

        FAIL  test/flatten.test.ts
         ● can handle empty arrays

           expect(received).toEqual(expected) // deep equality

           - Expected  - 1
           + Received  + 0

             Object {
               "a.b": "c",
           -   "d": Array [],
               "e.0": "f",
               "e.1": "g",
             }

             24 |     ],
             25 |     e: ['f', 'g'],
           > 26 |   })).toEqual({
                |       ^
             27 |     'a.b': 'c',
             28 |     'd': [],
             29 |     'e.0': 'f',

             at Object.<anonymous> (test/flatten.test.ts:26:7)

Which is unfortunate. I guess the best that can be done at the moment is to test if Payload.data is undefined even though that's not technically correct.

---

update

Well you also can't test for undefined because

invoke.assertAtPath('Payload.data', ExpectedResult.exact(undefined));

results in the error

Expected type object but received undefined