Put functional tests in `tests/functional`

I think it is bad for these reasons when `tests/` contains a mix of
functional and integration tests

 - Concepts is harder to understand, the documentation makes a good
   unit vs functional vs integration distinction, but when the
   integration tests are just two subdirs within `tests/` this is not
   clear.

 - Source filtering in the `flake.nix` is more complex. We need to
   filter out some of the dirs from `tests/`, rather than simply pick
   the dirs we want and take all of them. This is a good sign the
   structure of what we are trying to do is not matching the structure
   of the files.

With this change we have a clean:
```shell-session
$ git show 'HEAD:tests'
tree HEAD:tests

functional/
installer/
nixos/
```

(cherry picked from commit 68c81c737571794f7246db53fb4774e94fcf4b7e)

1 files changed, 26 insertions, 0 deletions

diff --git a/tests/functional/dyn-drv/text-hashed-output.sh b/tests/functional/dyn-drv/text-hashed-output.sh
new file mode 100644
index 000000000..f3e5aa93b
--- /dev/null
+++ b/tests/functional/dyn-drv/text-hashed-output.sh
@@ -0,0 +1,26 @@
+#!/usr/bin/env bash
+
+source common.sh
+
+# In the corresponding nix file, we have two derivations: the first, named root,
+# is a normal recursive derivation, while the second, named dependent, has the
+# new outputHashMode "text". Note that in "dependent", we don't refer to the
+# build output of root, but only to the path of the drv file. For this reason,
+# we only need to:
+#
+# - instantiate the root derivation
+# - build the dependent derivation
+# - check that the path of the output coincides with that of the original derivation
+
+drv=$(nix-instantiate ./text-hashed-output.nix -A hello)
+nix show-derivation "$drv"
+
+drvProducingDrv=$(nix-instantiate ./text-hashed-output.nix -A producingDrv)
+nix show-derivation "$drvProducingDrv"
+
+out1=$(nix-build ./text-hashed-output.nix -A producingDrv --no-out-link)
+
+nix path-info $drv --derivation --json | jq
+nix path-info $out1 --derivation --json | jq
+
+test $out1 == $drv