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, 70 insertions, 0 deletions

diff --git a/tests/functional/structured-attrs.nix b/tests/functional/structured-attrs.nix
new file mode 100644
index 000000000..e93139a44
--- /dev/null
+++ b/tests/functional/structured-attrs.nix
@@ -0,0 +1,70 @@
+with import ./config.nix;
+
+let
+
+  dep = mkDerivation {
+    name = "dep";
+    buildCommand = ''
+      mkdir $out; echo bla > $out/bla
+    '';
+  };
+
+in
+
+mkDerivation {
+  name = "structured";
+
+  __structuredAttrs = true;
+
+  outputs = [ "out" "dev" ];
+
+  buildCommand = ''
+    set -x
+
+    [[ $int = 123456789 ]]
+    [[ -z $float ]]
+    [[ -n $boolTrue ]]
+    [[ -z $boolFalse ]]
+    [[ -n ''${hardening[format]} ]]
+    [[ -z ''${hardening[fortify]} ]]
+    [[ ''${#buildInputs[@]} = 7 ]]
+    [[ ''${buildInputs[2]} = c ]]
+    [[ -v nothing ]]
+    [[ -z $nothing ]]
+
+    mkdir ''${outputs[out]} ''${outputs[dev]}
+    echo bar > $dest
+    echo foo > $dest2
+
+    json=$(cat $NIX_ATTRS_JSON_FILE)
+    [[ $json =~ '"narHash":"sha256:1r7yc43zqnzl5b0als5vnyp649gk17i37s7mj00xr8kc47rjcybk"' ]]
+    [[ $json =~ '"narSize":288' ]]
+    [[ $json =~ '"closureSize":288' ]]
+    [[ $json =~ '"references":[]' ]]
+  '';
+
+  buildInputs = [ "a" "b" "c" 123 "'" "\"" null ];
+
+  hardening.format = true;
+  hardening.fortify = false;
+
+  outer.inner = [ 1 2 3 ];
+
+  int = 123456789;
+
+  float = 123.456;
+
+  boolTrue = true;
+  boolFalse = false;
+
+  nothing = null;
+
+  dest = "${placeholder "out"}/foo";
+  dest2 = "${placeholder "dev"}/foo";
+
+  "foo bar" = "BAD";
+  "1foobar" = "BAD";
+  "foo$" = "BAD";
+
+  exportReferencesGraph.refs = [ dep ];
+}