vim-patch:8.2.2684: not enough folding code is tested

Problem:    Not enough folding code is tested.
Solution:   Add more test cases. (Yegappan Lakshmanan, closes vim/vim#8046)

https://github.com/vim/vim/commit/5c504f680e63120fea36becfabb8d939d4449e34

Reorder test_fold.vim to match upstream.
Cherry-pick Test_fold_expr_error() from patch 8.2.0633.
Cherry-pick syntax feature check from patch 8.2.1432.
Cherry-pick a delete() call from patch 8.2.2112.

1 files changed, 31 insertions, 0 deletions

diff --git a/test/functional/legacy/source_spec.lua b/test/functional/legacy/source_spec.lua
new file mode 100644
index 0000000000..02e6385247
--- /dev/null
+++ b/test/functional/legacy/source_spec.lua
@@ -0,0 +1,31 @@
+local helpers = require('test.functional.helpers')(after_each)
+local Screen = require('test.functional.ui.screen')
+local clear = helpers.clear
+local feed = helpers.feed
+local write_file = helpers.write_file
+
+before_each(clear)
+
+describe(':source!', function()
+  it('gives E22 when scripts nested too deep', function()
+    write_file('Xscript.vim', [[
+    :source! Xscript.vim
+    ]])
+    local screen = Screen.new(75, 6)
+    screen:set_default_attr_ids({
+      [0] = {bold = true, foreground = Screen.colors.Blue},  -- NonText
+      [1] = {background = Screen.colors.Red, foreground = Screen.colors.White},  -- ErrorMsg
+    })
+    screen:attach()
+    feed(':source! Xscript.vim\n')
+    screen:expect([[
+      ^                                                                           |
+      {0:~                                                                          }|
+      {0:~                                                                          }|
+      {0:~                                                                          }|
+      {0:~                                                                          }|
+      {1:E22: Scripts nested too deep}                                               |
+    ]])
+    os.remove('Xscript.vim')
+  end)
+end)