add details around how tests can be run; add .gvim_path file support

Author: jbodah

.gitignore

@@ -1,3 +1,4 @@
 profile.log
 test_indent.result
 doc/tags
+.gvim_path

README.md

@@ -87,9 +87,15 @@ If you get a lot of value from it, know vimscript well, or eager to learn about
 
 ### Running the Tests
 
-Run the tests: `bundle exec parallel_rspec spec`
+The tests depend on having Ruby installed.
+They also depend on a GUI vim (gvim, mvim) with server support.
+If you do not have gvim or mvim in your PATH then you can create a `.gvim_path` file in the vim-elixir root directory which specifies the path to the GUI vim executable.
 
-Spawn a container with vim and dev configs: `bin/vim` or `bin/nvim`
+To run the tests: `bundle exec parallel_rspec spec`
+
+### Developing in Docker
+
+You can spawn a container with vim and your development configs using `bin/vim` or `bin/nvim`
 
 ### Debugging Indent
 

spec/spec_helper.rb

@@ -3,6 +3,8 @@
 require 'vimrunner'
 require 'vimrunner/rspec'
 
+GVIM_PATH_FILE = File.expand_path('../../.gvim_path', __FILE__)
+
 class Buffer
   FOLD_PLACEHOLDER = '<!-- FOLD -->'.freeze
 
@@ -265,7 +267,12 @@ def self.new
   config.reuse_server = true
 
   config.start_vim do
-    VIM = Vimrunner.start_gvim
+    VIM =
+      if File.exists?(GVIM_PATH_FILE)
+        Vimrunner::Server.new(executable: File.read(GVIM_PATH_FILE).rstrip).start
+      else
+        Vimrunner.start_gvim
+      end
     VIM.add_plugin(File.expand_path('..', __dir__))
     cmd = ':filetype off<CR>'
     cmd += ':filetype plugin indent on<CR>'