fix(3p/nix/tests): Fail DummyStore::addToStore on non-existent srcPath r/1389

Unfortunately, to guarantee correct behaviour of some evaluation (!)
tests, addToStore needs to actually check whether passed in source
files exist and fail appropriately.

There is a chance that the dependency on this behaviour is actually a
bug in the upstream test suite, but my attempts at finding out more
about this from, say, the git history have so far been unsuccessful.

Change-Id: I311999ea28fcedf5da13a4e627b1c1c8e4e59cbd
Reviewed-on: https://cl.tvl.fyi/c/depot/+/1276
Reviewed-by: isomer <isomer@tvl.fyi>
Reviewed-by: glittershark <grfn@gws.fyi>
Tested-by: BuildkiteCI

0 files changed, 0 insertions, 0 deletions