patch 8.0.1539: no test for the popup menu positioning

Problem:    No test for the popup menu positioning.
Solution:   Add a screendump test for the popup menu.
diff --git a/src/testdir/test_popup.vim b/src/testdir/test_popup.vim
index d121aff..b0024e6 100644
--- a/src/testdir/test_popup.vim
+++ b/src/testdir/test_popup.vim
@@ -1,6 +1,7 @@
 " Test for completion menu
 
 source shared.vim
+source screendump.vim
 
 let g:months = ['January', 'February', 'March', 'April', 'May', 'June', 'July', 'August', 'September', 'October', 'November', 'December']
 let g:setting = ''
@@ -743,4 +744,37 @@
         \ 'struct = 0x234 {long = 2343 "\\"some long string that will be wrapped in two\\"", next = 123}'))
 endfunc
 
+func Test_popup_position()
+  if !CanRunVimInTerminal()
+    return
+  endif
+  call writefile([
+	\ '123456789_123456789_123456789_a',
+	\ '123456789_123456789_123456789_b',
+	\ '            123',
+	\ ], 'Xtest')
+  let buf = RunVimInTerminal('Xtest', {})
+  call term_sendkeys(buf, ":vsplit\<CR>")
+
+  " default pumwidth in left window: overlap in right window
+  call term_sendkeys(buf, "GA\<C-N>")
+  call VerifyScreenDump(buf, 'Test_popup_position_01', {'rows': 8})
+  call term_sendkeys(buf, "\<Esc>u")
+
+  " default pumwidth: fill until right of window
+  call term_sendkeys(buf, "\<C-W>l")
+  call term_sendkeys(buf, "GA\<C-N>")
+  call VerifyScreenDump(buf, 'Test_popup_position_02', {'rows': 8})
+
+  " larger pumwidth: used as minimum width
+  call term_sendkeys(buf, "\<Esc>u")
+  call term_sendkeys(buf, ":set pumwidth=30\<CR>")
+  call term_sendkeys(buf, "GA\<C-N>")
+  call VerifyScreenDump(buf, 'Test_popup_position_03', {'rows': 8})
+
+  call term_sendkeys(buf, "\<Esc>u")
+  call StopVimInTerminal(buf)
+  call delete('Xtest')
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab