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, 33 insertions, 0 deletions

diff --git a/tests/functional/build-remote-input-addressed.sh b/tests/functional/build-remote-input-addressed.sh
new file mode 100644
index 000000000..49d15c389
--- /dev/null
+++ b/tests/functional/build-remote-input-addressed.sh
@@ -0,0 +1,33 @@
+source common.sh
+
+file=build-hook.nix
+
+source build-remote.sh
+
+# Add a `post-build-hook` option to the nix conf.
+# This hook will be executed both for the local machine and the remote builders
+# (because they share the same config).
+registerBuildHook () {
+    # Dummy post-build-hook just to ensure that it's executed correctly.
+    # (we can't reuse the one from `$PWD/push-to-store.sh` because of
+    # https://github.com/NixOS/nix/issues/4341)
+    cat <<EOF > $TEST_ROOT/post-build-hook.sh
+#!/bin/sh
+
+echo "Post hook ran successfully"
+# Add an empty line to a counter file, just to check that this hook ran properly
+echo "" >> $TEST_ROOT/post-hook-counter
+EOF
+    chmod +x $TEST_ROOT/post-build-hook.sh
+    rm -f $TEST_ROOT/post-hook-counter
+
+    echo "post-build-hook = $TEST_ROOT/post-build-hook.sh" >> $NIX_CONF_DIR/nix.conf
+}
+
+registerBuildHook
+source build-remote.sh
+
+# `build-hook.nix` has four derivations to build, and the hook runs twice for
+# each derivation (once on the builder and once on the host), so the counter
+# should contain eight lines now
+[[ $(cat $TEST_ROOT/post-hook-counter | wc -l) -eq 8 ]]