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I've found unit testing to work fine for Lambdas. The biggest difference between running as a Lambda and running locally is the entry point. With a Lambda you have an event payload that (usually) needs to be parsed and evaluated.

I'll typically write all the core functionality first, test it, then write the lambda_handler function.

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But how do you test lamba_handler then? Without a way to run lambdas locally, this sounds like a big black hole in your infrastructure.

You call it just like you call any other function. Your handler takes in either a JSON payload and a context object or a deserialized object depending on the language. You call it from a separate console app, your test harness etc.

Yup. You can log into the AWS console and generate an example test message. Copy that into your unit/integration test and bob's your uncle.

We deploy to a test stack and run a full integration test of the code running in AWS. I believe it's also possible to self-host locally, but we never really looked into it.

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