I have detailed knowledge of dynamodb. This code does not properly mimic the service exceptions, input validations, eventual consistency, or edge cases. I would not feel comfortable developing against ministack or running tests against it. A lot of these services also have free tiers, so the use cases are quite minimal.
Hello! The target use case is integration testing, verifying that your application calls the right operations with the right data, not production fidelity. For that, MiniStack works well and is free. For anything requiring exact DynamoDB behavior (capacity throttling, consistency window, stream processing), you're right that it's not a substitute. Contributions to improve error fidelity are very welcome (we have pending ProvisionedThroughputExceededException, TransactionConflictException, ItemCollectionSizeLimitExceededException)
Mostly I think its not about cost, it is about iteration speed and ability to run in CI environments fast.
Neither does localstack to be fair.