tests: add cleanup logic for changed nix-channels

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

@@ -2,7 +2,15 @@
 
 load lib
 
+setup() {
+  _setup
+  cp ~/.nix-channels ~/.nix-channels.bak
+}
+
 teardown() {
+  nix-channel --remove home-manager
+  mv ~/.nix-channels.bak ~/.nix-channels
+
   rm -f ~/.config/example
 }
 

tests/on-device/lib.bash

@@ -1,6 +1,7 @@
 # Copyright (c) 2019-2021, see AUTHORS. Licensed under MIT License, see LICENSE.
 
-setup() {
+# call _setup when defining a setup function in your test
+_setup() {
   if [[ -z "$ON_DEVICE_TESTS_SETUP" ]]; then
     CHANNEL_DIR="$(nix-instantiate --eval --expr '<nix-on-droid>')"
     ON_DEVICE_TESTS_DIR="$CHANNEL_DIR/tests/on-device"
@@ -33,6 +34,10 @@ setup() {
   switch_to_default_config
 }
 
+setup() {
+  _setup
+}
+
 assert_command() {
   for cmd_name; do
     command -v "$cmd_name"