ValidationException when calling the InvokeAgent operation

Following error is produced when testing a Bedrock agent:
```
ERROR Error running test: An error occurred (ValidationException) when calling the InvokeAgent operation: Either of inputText or invocationResult with invocationId must be non-empty
```

Start by reproducing the Bedrock agent test that calls InvokeAgent and inspect how inputText and invocationResult are supplied. Trace the request inputs around the failing operation and compare them with the validation error; done means the test completes without this ValidationException and the relevant behavior is covered.

Written by the indexing model from the issue text.