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, 0 insertions, 147 deletions

diff --git a/tests/nix-shell.sh b/tests/nix-shell.sh
deleted file mode 100644
index edaa1249b..000000000
--- a/tests/nix-shell.sh
+++ /dev/null
@@ -1,147 +0,0 @@
-source common.sh
-
-clearStore
-
-if [[ -n ${CONTENT_ADDRESSED:-} ]]; then
-    shellDotNix="$PWD/ca-shell.nix"
-else
-    shellDotNix="$PWD/shell.nix"
-fi
-
-export NIX_PATH=nixpkgs="$shellDotNix"
-
-# Test nix-shell -A
-export IMPURE_VAR=foo
-export SELECTED_IMPURE_VAR=baz
-
-output=$(nix-shell --pure "$shellDotNix" -A shellDrv --run \
-    'echo "$IMPURE_VAR - $VAR_FROM_STDENV_SETUP - $VAR_FROM_NIX - $TEST_inNixShell"')
-
-[ "$output" = " - foo - bar - true" ]
-
-# Test --keep
-output=$(nix-shell --pure --keep SELECTED_IMPURE_VAR "$shellDotNix" -A shellDrv --run \
-    'echo "$IMPURE_VAR - $VAR_FROM_STDENV_SETUP - $VAR_FROM_NIX - $SELECTED_IMPURE_VAR"')
-
-[ "$output" = " - foo - bar - baz" ]
-
-# Test nix-shell on a .drv
-[[ $(nix-shell --pure $(nix-instantiate "$shellDotNix" -A shellDrv) --run \
-    'echo "$IMPURE_VAR - $VAR_FROM_STDENV_SETUP - $VAR_FROM_NIX - $TEST_inNixShell"') = " - foo - bar - false" ]]
-
-[[ $(nix-shell --pure $(nix-instantiate "$shellDotNix" -A shellDrv) --run \
-    'echo "$IMPURE_VAR - $VAR_FROM_STDENV_SETUP - $VAR_FROM_NIX - $TEST_inNixShell"') = " - foo - bar - false" ]]
-
-# Test nix-shell on a .drv symlink
-
-# Legacy: absolute path and .drv extension required
-nix-instantiate "$shellDotNix" -A shellDrv --add-root $TEST_ROOT/shell.drv
-[[ $(nix-shell --pure $TEST_ROOT/shell.drv --run \
-    'echo "$IMPURE_VAR - $VAR_FROM_STDENV_SETUP - $VAR_FROM_NIX"') = " - foo - bar" ]]
-
-# New behaviour: just needs to resolve to a derivation in the store
-nix-instantiate "$shellDotNix" -A shellDrv --add-root $TEST_ROOT/shell
-[[ $(nix-shell --pure $TEST_ROOT/shell --run \
-    'echo "$IMPURE_VAR - $VAR_FROM_STDENV_SETUP - $VAR_FROM_NIX"') = " - foo - bar" ]]
-
-# Test nix-shell -p
-output=$(NIX_PATH=nixpkgs="$shellDotNix" nix-shell --pure -p foo bar --run 'echo "$(foo) $(bar)"')
-[ "$output" = "foo bar" ]
-
-# Test nix-shell -p --arg x y
-output=$(NIX_PATH=nixpkgs="$shellDotNix" nix-shell --pure -p foo --argstr fooContents baz --run 'echo "$(foo)"')
-[ "$output" = "baz" ]
-
-# Test nix-shell shebang mode
-sed -e "s|@ENV_PROG@|$(type -P env)|" shell.shebang.sh > $TEST_ROOT/shell.shebang.sh
-chmod a+rx $TEST_ROOT/shell.shebang.sh
-
-output=$($TEST_ROOT/shell.shebang.sh abc def)
-[ "$output" = "foo bar abc def" ]
-
-# Test nix-shell shebang mode again with metacharacters in the filename.
-# First word of filename is chosen to not match any file in the test root.
-sed -e "s|@ENV_PROG@|$(type -P env)|" shell.shebang.sh > $TEST_ROOT/spaced\ \\\'\"shell.shebang.sh
-chmod a+rx $TEST_ROOT/spaced\ \\\'\"shell.shebang.sh
-
-output=$($TEST_ROOT/spaced\ \\\'\"shell.shebang.sh abc def)
-[ "$output" = "foo bar abc def" ]
-
-# Test nix-shell shebang mode for ruby
-# This uses a fake interpreter that returns the arguments passed
-# This, in turn, verifies the `rc` script is valid and the `load()` script (given using `-e`) is as expected.
-sed -e "s|@SHELL_PROG@|$(type -P nix-shell)|" shell.shebang.rb > $TEST_ROOT/shell.shebang.rb
-chmod a+rx $TEST_ROOT/shell.shebang.rb
-
-output=$($TEST_ROOT/shell.shebang.rb abc ruby)
-[ "$output" = '-e load(ARGV.shift) -- '"$TEST_ROOT"'/shell.shebang.rb abc ruby' ]
-
-# Test nix-shell shebang mode for ruby again with metacharacters in the filename.
-# Note: fake interpreter only space-separates args without adding escapes to its output.
-sed -e "s|@SHELL_PROG@|$(type -P nix-shell)|" shell.shebang.rb > $TEST_ROOT/spaced\ \\\'\"shell.shebang.rb
-chmod a+rx $TEST_ROOT/spaced\ \\\'\"shell.shebang.rb
-
-output=$($TEST_ROOT/spaced\ \\\'\"shell.shebang.rb abc ruby)
-[ "$output" = '-e load(ARGV.shift) -- '"$TEST_ROOT"'/spaced \'\''"shell.shebang.rb abc ruby' ]
-
-# Test 'nix develop'.
-nix develop -f "$shellDotNix" shellDrv -c bash -c '[[ -n $stdenv ]]'
-
-# Ensure `nix develop -c` preserves stdin
-echo foo | nix develop -f "$shellDotNix" shellDrv -c cat | grepQuiet foo
-
-# Ensure `nix develop -c` actually executes the command if stdout isn't a terminal
-nix develop -f "$shellDotNix" shellDrv -c echo foo |& grepQuiet foo
-
-# Test 'nix print-dev-env'.
-
-nix print-dev-env -f "$shellDotNix" shellDrv > $TEST_ROOT/dev-env.sh
-nix print-dev-env -f "$shellDotNix" shellDrv --json > $TEST_ROOT/dev-env.json
-
-# Test with raw drv
-
-shellDrv=$(nix-instantiate "$shellDotNix" -A shellDrv.out)
-
-nix develop $shellDrv -c bash -c '[[ -n $stdenv ]]'
-
-nix print-dev-env $shellDrv > $TEST_ROOT/dev-env2.sh
-nix print-dev-env $shellDrv --json > $TEST_ROOT/dev-env2.json
-
-diff $TEST_ROOT/dev-env{,2}.sh
-diff $TEST_ROOT/dev-env{,2}.json
-
-# Ensure `nix print-dev-env --json` contains variable assignments.
-[[ $(jq -r .variables.arr1.value[2] $TEST_ROOT/dev-env.json) = '3 4' ]]
-
-# Run tests involving `source <(nix print-dev-inv)` in subshells to avoid modifying the current
-# environment.
-
-set +u # FIXME: Make print-dev-env `set -u` compliant (issue #7951)
-
-# Ensure `source <(nix print-dev-env)` modifies the environment.
-(
-    path=$PATH
-    source $TEST_ROOT/dev-env.sh
-    [[ -n $stdenv ]]
-    [[ ${arr1[2]} = "3 4" ]]
-    [[ ${arr2[1]} = $'\n' ]]
-    [[ ${arr2[2]} = $'x\ny' ]]
-    [[ $(fun) = blabla ]]
-    [[ $PATH = $(jq -r .variables.PATH.value $TEST_ROOT/dev-env.json):$path ]]
-)
-
-# Ensure `source <(nix print-dev-env)` handles the case when PATH is empty.
-(
-    path=$PATH
-    PATH=
-    source $TEST_ROOT/dev-env.sh
-    [[ $PATH = $(PATH=$path jq -r .variables.PATH.value $TEST_ROOT/dev-env.json) ]]
-)
-
-# Test nix-shell with ellipsis and no `inNixShell` argument (for backwards compat with old nixpkgs)
-cat >$TEST_ROOT/shell-ellipsis.nix <<EOF
-{ system ? "x86_64-linux", ... }@args:
-assert (!(args ? inNixShell));
-(import $shellDotNix { }).shellDrv
-EOF
-nix-shell $TEST_ROOT/shell-ellipsis.nix --run "true"