[tmux] Add remote session nesting

If calling a tmux session within a tmux session, pressing F12 will
toggle between sending commands to the outer or inner session. If the
outer session is inactive its status-bar will be slightly greyed out to
show that no commands will reach it. If the inner session is a remote
ssh session, it will set some additional stylings for the status-bar to
further differentiate the two.

.local/bin/test/tm.bats

@@ -0,0 +1,39 @@
+setup() {
+  fut="$BATS_TEST_DIRNAME/../tm"
+}
+
+teardown() {
+  rm -rf $BATS_TMPDIR/xdg/*
+}
+
+@test "runs correctly if invoked without arguments" {
+  run $fut
+  echo "$BATS_TEST_DIRNAME/../tm"
+  [ "$status" -eq 0 ]
+}
+
+@test "Errors out if passed a non-existent session file (and some session name)" {
+  run $fut IDONT_EXIST_HERE.session sessionname
+  echo "STATUS: $output"
+  [ "$status" -eq 1 ]
+  echo "OUTPUT: $output"
+  [ "$output" = "can not source session file: 'IDONT_EXIST_HERE.session' does not exist." ]
+}
+
+@test "Runs without errors when session file exists in PWD" {
+  touch $PWD/exists.session
+  run $fut exists.session sessionname
+  rm $PWD/exists.session
+
+  [ "$status" -eq 0 ]
+}
+
+@test "Runs without errors when session file exists in XDG_CONFIG_HOME/tmux/sessions/" {
+  export XDG_CONFIG_HOME=$BATS_TMPDIR
+  mkdir -p $XDG_CONFIG_HOME/tmux/sessions
+  sesdir=$XDG_CONFIG_HOME/tmux/sessions
+  touch $sesdir/exists.session
+  run $fut exists.session sessionname
+
+  [ "$status" -eq 0 ]
+}