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, 123 insertions, 0 deletions

diff --git a/tests/functional/repair.sh b/tests/functional/repair.sh
new file mode 100644
index 000000000..c8f07b1c6
--- /dev/null
+++ b/tests/functional/repair.sh
@@ -0,0 +1,123 @@
+source common.sh
+
+needLocalStore "--repair needs a local store"
+
+clearStore
+
+path=$(nix-build dependencies.nix -o $TEST_ROOT/result)
+path2=$(nix-store -qR $path | grep input-2)
+
+nix-store --verify --check-contents -v
+
+hash=$(nix-hash $path2)
+
+# Corrupt a path and check whether nix-build --repair can fix it.
+chmod u+w $path2
+touch $path2/bad
+
+(! nix-store --verify --check-contents -v)
+
+# The path can be repaired by rebuilding the derivation.
+nix-store --verify --check-contents --repair
+
+(! [ -e $path2/bad ])
+(! [ -w $path2 ])
+
+nix-store --verify-path $path2
+
+# Re-corrupt and delete the deriver. Now --verify --repair should
+# not work.
+chmod u+w $path2
+touch $path2/bad
+
+nix-store --delete $(nix-store -q --referrers-closure $(nix-store -qd $path2))
+
+(! nix-store --verify --check-contents --repair)
+
+nix-build dependencies.nix -o $TEST_ROOT/result --repair
+
+if [ "$(nix-hash $path2)" != "$hash" -o -e $path2/bad ]; then
+    echo "path not repaired properly" >&2
+    exit 1
+fi
+
+# Corrupt a path that has a substitute and check whether nix-store
+# --verify can fix it.
+clearCache
+
+nix copy --to file://$cacheDir $path
+
+chmod u+w $path2
+rm -rf $path2
+
+nix-store --verify --check-contents --repair --substituters "file://$cacheDir" --no-require-sigs
+
+if [ "$(nix-hash $path2)" != "$hash" -o -e $path2/bad ]; then
+    echo "path not repaired properly" >&2
+    exit 1
+fi
+
+# Check --verify-path and --repair-path.
+nix-store --verify-path $path2
+
+chmod u+w $path2
+rm -rf $path2
+
+if nix-store --verify-path $path2; then
+    echo "nix-store --verify-path succeeded unexpectedly" >&2
+    exit 1
+fi
+
+nix-store --repair-path $path2 --substituters "file://$cacheDir" --no-require-sigs
+
+if [ "$(nix-hash $path2)" != "$hash" -o -e $path2/bad ]; then
+    echo "path not repaired properly" >&2
+    exit 1
+fi
+
+# Check that --repair-path also checks content of optimised symlinks (1/2)
+nix-store --verify-path $path2
+
+if (! nix-store --optimize); then
+    echo "nix-store --optimize failed to optimize the store" >&2
+    exit 1
+fi
+chmod u+w $path2/bar
+echo 'rabrab' > $path2/bar # different length
+
+if nix-store --verify-path $path2; then
+    echo "nix-store --verify-path did not detect .links file corruption" >&2
+    exit 1
+fi
+
+nix-store --repair-path $path2 --option auto-optimise-store true
+
+if [ "$(nix-hash $path2)" != "$hash" -o "BAR" != "$(< $path2/bar)" ]; then
+    echo "path not repaired properly" >&2
+    exit 1
+fi
+
+# Check that --repair-path also checks content of optimised symlinks (2/2)
+nix-store --verify-path $path2
+
+if (! nix-store --optimize); then
+    echo "nix-store --optimize failed to optimize the store" >&2
+    exit 1
+fi
+chmod u+w $path2
+chmod u+w $path2/bar
+sed -e 's/./X/g' < $path2/bar > $path2/tmp # same length, different content.
+cp $path2/tmp $path2/bar
+rm $path2/tmp
+
+if nix-store --verify-path $path2; then
+    echo "nix-store --verify-path did not detect .links file corruption" >&2
+    exit 1
+fi
+
+nix-store --repair-path $path2 --substituters "file://$cacheDir" --no-require-sigs --option auto-optimise-store true
+
+if [ "$(nix-hash $path2)" != "$hash" -o "BAR" != "$(< $path2/bar)" ]; then
+    echo "path not repaired properly" >&2
+    exit 1
+fi