Setup a plugin.
  
    $ mkdir plugin
  
  A git wrapper that works with the plugin's repo.
  
    $ pg () {
    >   git --git-dir plugin/.git --work-tree plugin "$@"
    > }
  
  Setup the plugin repo.
  
    $ pg init
    Initialized empty Git repository in .+?/plugin/\.git/? (re)
  
  Master branch content.
  
    $ cat > plugin/aliases.zsh <<EOF
    > alias hehe='echo hehe'
    > EOF
    $ pg add .
    $ pg commit -m 'Initial commit'
    \[master \(root-commit\) [a-f0-9]{7}\] Initial commit (re)
     1 file changed, 1 insertion(+)
     create mode [\d]{6} aliases\.zsh (re)
  
  Branch b1.
  
    $ pg branch b1
    $ pg checkout b1
    Switched to branch 'b1'
    $ cat > plugin/aliases.zsh <<EOF
    > alias hehe='echo hehe from b1'
    > EOF
    $ pg commit -am 'Change for b1'
    \[b1 [a-f0-9]{7}\] Change for b1 (re)
     1 file changed, 1 insertion(+), 1 deletion(-)
  
  Go back to master.
  
    $ pg checkout master
    Switched to branch 'master'
  
  Load plugin from b1.
  
    $ antigen-bundle $PWD/plugin --branch=b1
    Cloning into '.+?'\.\.\. (re)
    done.
    Switched to a new branch 'b1'
    Branch b1 set up to track remote branch b1 from origin.
    $ hehe
    hehe from b1
  
  Load plugin from master.
  
    $ antigen-bundle $PWD/plugin
    Cloning into '.+?'\.\.\. (re)
    done.
    $ hehe
    hehe