Add NERDTree tests

tests/test_nerdtree_plugin.vim

@@ -0,0 +1,11 @@
+#!/usr/bin/vim -S
+set nocompatible
+set columns=80
+execute 'source' fnameescape(expand('<sfile>:p:h').'/vim_utils.vim')
+call EnablePlugins('nerdtree')
+call SourcePowerline()
+NERDTree /home
+redrawstatus
+call CheckCurrentStatusline('%#Pl_231_16777215_240_5789784_bold# /home %#Pl_240_5789784_236_3158064_NONE# %#Pl_231_16777215_236_3158064_NONE#                      ')
+call CheckMessages()
+qall

tests/vim_utils.vim

@@ -46,6 +46,15 @@ endfunction
 function CheckRecordedStatuslineValue(expected)
 	return CheckStatuslineValue(g:statusline_value, a:expected)
 endfunction
+function GetCurrentStatusline()
+	if &l:statusline[:1] isnot# '%!'
+		ERR 'Statusline does not start with %!', &l:statusline
+	endif
+	return eval(&l:statusline[2:])
+endfunction
+function CheckCurrentStatusline(expected)
+	return CheckStatuslineValue(GetCurrentStatusline(), a:expected)
+endfunction
 function CheckMessages()
 	if !empty(g:powerline_log_messages)
 		LST ['Unexpected messages in log'] + g:powerline_log_messages