patch 8.0.0525: completion for user command argument not tested

Solution:   Completion for user command argument not tested.
Problem:    Add a test.

src/testdir/test_cmdline.vim

@@ -348,6 +348,15 @@ func Test_cmdline_complete_wildoptions()
   bw!
 endfunc
 
+func Test_cmdline_complete_user_cmd()
+  command! -complete=color -nargs=1 Foo :
+  call feedkeys(":Foo \<Tab>\<Home>\"\<cr>", 'tx')
+  call assert_equal('"Foo blue', @:)
+  call feedkeys(":Foo b\<Tab>\<Home>\"\<cr>", 'tx')
+  call assert_equal('"Foo blue', @:)
+  delcommand Foo
+endfunc
+
 " using a leading backslash here
 set cpo+=C
 

src/version.c

@@ -764,6 +764,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    525,
 /**/
     524,
 /**/