test the layout config for the default extension.

.gitignore

@@ -1,2 +1,3 @@
 doc/tags
 *.lock
+.vim-flavor

autoload/airline/extensions/branch.vim

@@ -27,7 +27,9 @@ function! airline#extensions#branch#get_head()
     endif
   endif
 
-  return empty(head) ? s:empty_message : s:symbol.' '.head
+  return empty(head)
+        \ ? s:empty_message
+        \ : printf('%s%s', empty(s:symbol) ? '' : s:symbol.' ', head)
 endfunction
 
 function! airline#extensions#branch#init(ext)

t/extensions_default.vim

@@ -0,0 +1,22 @@
+call airline#init#bootstrap()
+
+describe 'default'
+  before
+    let s:builder = airline#builder#new({'active': 1})
+  end
+
+  it 'should use the layout'
+    let g:airline#extensions#default#layout = [
+          \ [ 'c', 'a', 'b', 'warning' ],
+          \ [ 'x', 'z', 'y' ]
+          \ ]
+    call airline#extensions#default#apply(s:builder, { 'winnr': 1, 'active': 1 })
+    let stl = s:builder.build()
+    Expect stl =~ 'airline_c_to_airline_a'
+    Expect stl =~ 'airline_a_to_airline_b'
+    Expect stl =~ 'airline_b_to_airline_warning'
+    Expect stl =~ 'airline_x_to_airline_z'
+    Expect stl =~ 'airline_z_to_airline_y'
+  end
+end
+