fix: mock Agent querying OS for listening ports in tests #20842
Merged
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fixes coder/internal#1123
We want to tests that ports are not included after they are no longer used, but this isn't safe on the real OS networking stack because there is no way to guarantee a port won't be used. Instead, we introduce an interface and fake implementation for testing.
On order to leave the filtering logic in the test path, this PR also does some refactoring.
Caching logic is left in the real OS querying implementation and a new test case is added for it in this PR.