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Do you mind adding a unit test to https://github.com/Microsoft/TypeScript/blob/master/tests/cases/unittests/tsconfigParsing.ts

I would like to do so, but its a bit tricky.
My proposed fix is a quickfix for the readDirectory function from sys.ts (here and here). In tsconfigParsing.ts this specific part (the buggy code) is mocked away, so no chance to test it :(

Explanation:
All occurrences of

const name = combinePaths(path, current);

use the wrong (non-normalized) path. I wil change my PR to fix the concrete bug, but I don't know how to test this, because there is no test for readDirectory or sys.ts at all!?

Btw: I know nothing about the WScript subsystem, so maybe this fix is only needed for the Node subsystem.

Superseded by #12667