The node level tests can benefit from this helper. For now I have excluded it from common, and server-common, because those tests should execute outside node without many polyfills or dependencies if we need them to. We may be able to more widely use them later.

There are some node level big segments test for the event emitter implementation. The main testing is done in the common sdk.

Most of the file data source testing is at the common level, but here we make sure it works with the actual node filesystem APIs.

If it's just the I/O implementation that's distinctive here, I feel like you might be able to make the tests a bit simpler by omitting things like the segment. I mean, the fact that there's a flag referencing a segment is a detail of the data that's in the file, which should be orthogonal to how we read the file or detected changes to the file.

Primarily for the event emitter connection.

Moved to follow directory structure.

Moved to follow directory structure.

If it's just the I/O implementation that's distinctive here, I feel like you might be able to make the tests a bit simpler by omitting things like the segment. I mean, the fact that there's a flag referencing a segment is a detail of the data that's in the file, which should be orthogonal to how we read the file or detected changes to the file.

Something that's occurred to me during this reviews in general is that the large number of LDClientImpl constructor parameters makes it a bit hard to see which one is which. Might you consider creating a type whose only purpose is to make some of these into named properties? Like, the first three parameters are mandatory and generally self-explanatory at the call site, but these other callbacks not so much. If the usage were something like this—

    new LDClientImpl(
      sdkKey,
      platform,
      config,
      {
        hasEventListeners: () => true
      });

—it'd be easier to see what's happening, and possibly harder to make a mistake by putting parameters in the wrong order. In this example I've assumed that there is some default behavior for the unspecified ones, which might not make sense in a non-test context since (I think) all of the SDK implementations are likely to need to provide all of those callbacks, but even if they're all mandatory & therefore can't make the test code less verbose, I feel like there might be some benefit.

I've implemented this change.

It does remove some verbosity in tests, because I added a makeCallbacks(withEvents:boolean) helper that most tests can use.

Just a thought for future test writing: something I've done in other SDKs, and wish I had gotten around to in Node, is to rely more heavily on helper functions for generating boilerplate pieces of flag configuration like this. For instance, if the idea is to make a clause that will definitely match this user, I would change this to something like clauses: [clauseThatMatchesUser(defaultUser)] and define clauseThatMatchesUser to be equivalent to this. Even though this kind of logic isn't rocket science and isn't incredibly verbose, I find that it's easier for me to understand and validate the test logic at a glance when there are fewer extraneous details and I can see the intention immediately from the names of things, rather than having to infer it from my knowledge of how such a clause would be evaluated.