Deno: Test Case Is Leaking Resources.

E Ozcelik
E Ozcelik
Sep 12, 2020 · 2 min read


Recently, I have been working on an open-source Deno project centered around automatically generating documentation for your code based on your tests.

During the testing process, particularly, when Deno interacts with external resources, I was getting a strange error that looked like this :


This is caused by Deno’s internal architecture which holds a record of open files, sockets and other concepts.

You can close a single resource by its RID :

Some functions provide easy access to this RID id. For example:

Then, some other functions expose methods to close the resource internally :

However, some functions are not that easy to handle. For example, Deno.createSync() does not return a handle for the opened resource. For these kind of situations, at any moment in a Deno program, you can get a list of open resources to target specific resources or iterate over all open resources.

If you are looking for a quick solution for your tests without messing with RID ids, you can simply ignore this mechanism by restructuring your tests as follows:


Being a new technology, it was somewhat hard to get a clear answer. As always, a Stackoverflow question was one of the few pertinent elements:

Then, of course, there is the official documentation which provides more clarification.

Unfortunate that the documentation doesn’t appear among the top results during a Google search. Also, this problem is discussed only within the context of testing but I would assume this is as much relevant for your run-of-the-mill Deno project to prevent memory leaks. If you think otherwise, don’t hesitate share with me.

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