I can add a test case. Could you point me to some test cases that test similar code paths? I wasn't able to find any.

Regarding changing behavior in response to the new assert, it seems that the code already reflects the possibility of this new assert. For example, line 1789, which would be hit given this change, already handles dynamic files. The line you pointed out, 1791, is unaffected by this change, since this assert is already true if openedByClient is true.

Disregard my request for finding tests; I'll add a test to tsserverProjectSystem.ts.

Regarding changing behavior in response to the new assert, it seems that the code already reflects the possibility of this new assert. For example, line 1789, which would be hit given this change, already handles dynamic files. The line you pointed out, 1791, is unaffected by this change, since this assert is already true if openedByClient is true.

What i meant is that if in your test case if you change projectFileName to say /a/b/c/someproj,proj you will have a problem. openFilesWithNonRootedDiskPath handles when the file name is not a rooted file name. The identity of the file would be mismatched by project and its program.. Program assumes the identity for non rooted file path by using currentDirectory + nonRooted file name (dynamic file is still non rooted from program's perspective). Since the current directory for the project depends on whats being supplied (if not valid name it is location of tsserver which is what your test case does at moment and hence you don't really see the issue that assert was validating) in that case the identity of the file would be /a/b/c/^ScriptDocument1 file1.ts but when you open file it wont match and would be something like /^ScriptDocument1 file1.ts and it wont find the external project. So this needs more work than just fixing assert

Understood. I will try to match the test case closer to what VS is actually calling and see what I might need to update.

After discussing separately with @sheetalkamat, I added another assertion explaining that dynamic script infos will always share the same name and project file name, and therefore will always have the tsserver location as the current directory.