Yes, I inherited a Lambda code-base too, and it is an absolute knot - Lambdas sending requests to other Lambdas, Lambdas sending messages and other Lambdas reading the messages, Lambdas reading and disregarding messages due to poorly thought-out queues etc.
I remember at one job, they were talking about the overall architecture of code at the company and when I asked how can I run this on my computer, they said well you can just run it but I pushed... How can I run this whole thing on my computer to interact with everything else and it was met with silence.
I can understand having to stub out external calls to vendors and clients but this is ridiculous. There is no local story.
Oh yeah I have a lambda that needs another lambda to complete before running. The first is on a Cloudwatch event interval. So the data in the second can be stale, but the one saving grace of the situation is that no one cares enough to make me fix it, not even me.
And of course, no easy way to test locally.