don't raise an error for no server file if testing

Author: ankhers

Diff for: lib/guard/go/runner.rb

@@ -10,7 +10,9 @@ class GoRunner
     def initialize(options)
       @options = options
 
-      raise "Server file not found. Check your :server option in your Guardfile." unless File.exists? @options[:server]
+      unless @options[:test] && File.exists?(@options[:server])
+        raise "Server file not found. Check your :server option in your Guardfile."
+      end
     end
 
     def start