which communicates your intent to the compiler

Now consider we want to handle numbers in our known value set: const KNOWN_VALUES = Object.freeze(['a', 'b', 'c', 1, 2, 3]) function isKnownValue(input?: string | number) { return typeof(input) === 'string' && KNOWN_VALUES.includes(input) } Uh oh! This TypeScript compiles without errors, but it's not correct. Where as our original "naive" approach would have worked just fine. Why is that? Where is the breakdown here? It's because TypeScript's type system got in the way of the developer's initial intent. It caused us to change our code from what we intended to what it allowed. It was never the developer's intention to check that input was a string and a known value; the developer simply wanted to check whether input was a known value - but wasn't permitted to do so.

You might get the impression after reading David's article above that this trend arose from lazy developers who "forgot how to program", but the reality is that the tiny-module ecosystem on NPM was the intention from the beginning

ECMAScript 6th Edition (ECMA-262) introduces template literals which are intended to be used for embedding DSL in ECMAScript.

(After all, it's not like the past snapshot was well understood or carefully expressed authorial intent.) As a result, if a snapshot test fails because some intended behavior disappeared, then there's little stated intention describing it and we'd much rather regenerate the file than spend a lot of time agonizing over how to get the same test green again.

Good tests encode the developer's intention, they don't only lock in the test's behavior without editorialization of what's important and why. Snapshot tests lack (or at least, fail to encourage) expressing the author's intent as to what the code does (much less why)