tests: increase readability through small helper functions

tests/on-device/config-flake-h-m.bats

@@ -10,10 +10,9 @@ load lib
   # set up / build / activate the configuration
   cat "$ON_DEVICE_TESTS_DIR/config-flake-h-m.cfg.nix" \
     > ~/.config/nixpkgs/nix-on-droid.nix
-  nix-shell -p gnused --run \
-    "sed 's|<<FLAKE_URL>>|$FLAKE_URL|g' \
-         < '$ON_DEVICE_TESTS_DIR/config-flake-h-m.flake.nix' \
-         > ~/.config/nixpkgs/flake.nix"
+  _sed "s|<<FLAKE_URL>>|$FLAKE_URL|g" \
+    "$ON_DEVICE_TESTS_DIR/config-flake-h-m.flake.nix" \
+    > ~/.config/nixpkgs/flake.nix
   pushd ~/.config/nixpkgs
     nix-shell -p nixFlakes --run \
       'nix build \

tests/on-device/config-flake.bats

@@ -8,17 +8,15 @@ load lib
   assert_no_command unzip
 
   # set up / build / activate the configuration
-  nix-shell -p gnused --run \
-    "sed \
-         -e s/vim/nano/ \
-         -e s/#unzip/unzip/ \
-         < '$CHANNEL_DIR/modules/environment/login/nix-on-droid.nix.default' \
-         > ~/.config/nixpkgs/nix-on-droid.nix"
+  _sed \
+    -e 's/vim/nano/' \
+    -e 's/#unzip/unzip/' \
+    "$CHANNEL_DIR/modules/environment/login/nix-on-droid.nix.default" \
+    > ~/.config/nixpkgs/nix-on-droid.nix
 
-  nix-shell -p gnused --run \
-    "sed 's|<<FLAKE_URL>>|$FLAKE_URL|g' \
-         < '$ON_DEVICE_TESTS_DIR/config-flake.nix' \
-         > ~/.config/nixpkgs/flake.nix"
+  _sed "s|<<FLAKE_URL>>|$FLAKE_URL|g" \
+    "$ON_DEVICE_TESTS_DIR/config-flake.nix" \
+    > ~/.config/nixpkgs/flake.nix
 
   # this is more cumbersome than options,
   # but this is what we recommend to users, so taking the hard way

tests/on-device/gnumake.bats

@@ -4,7 +4,9 @@
   TEMPDIR=/tmp/.tmp-gnumake.$$
   mkdir -p "$TEMPDIR"
   echo -e 'x:\n\techo desired output > x' > "$TEMPDIR/Makefile"
-  nix-shell -p gnumake --run "make -C $TEMPDIR x"
+
+  "$(nix-build "<nixpkgs>" --no-out-link --attr gnumake)/bin/make" -C "$TEMPDIR" x
+
   [[ -e "$TEMPDIR/x" ]]
   [[ "$(cat "$TEMPDIR/x")" == 'desired output' ]]
 }

tests/on-device/lib.bash

@@ -51,3 +51,9 @@ switch_to_default_config() {
     > ~/.config/nixpkgs/nix-on-droid.nix
   nix-on-droid switch
 }
+
+_sed() {
+  local storePath
+  storePath="$(nix-build "<nixpkgs>" --no-out-link --attr gnused)"
+  "${storePath}/bin/sed" "$@"
+}