test: output_spec

Reference: https://github.com/neovim/neovim/issues/3772#issuecomment-162334005

test/functional/ui/output_spec.lua

@@ -0,0 +1,39 @@
+local session = require('test.functional.helpers')(after_each)
+local child_session = require('test.functional.terminal.helpers')
+
+describe("shell command :!", function()
+  local screen
+  before_each(function()
+    session.clear()
+    screen = child_session.screen_setup(0, '["'..session.nvim_prog..
+      '", "-u", "NONE", "-i", "NONE", "--cmd", "set noswapfile"]')
+    screen:expect([[
+      {1: }                                                 |
+      ~                                                 |
+      ~                                                 |
+      ~                                                 |
+      [No Name]                                         |
+                                                        |
+      -- TERMINAL --                                    |
+    ]])
+  end)
+
+  after_each(function()
+    screen:detach()
+  end)
+
+  it("displays output even without LF/EOF. #4646 #4569 #3772", function()
+    -- NOTE: We use a child nvim (within a :term buffer)
+    --       to avoid triggering a UI flush.
+    child_session.feed_data(":!printf foo; sleep 200\n")
+    screen:expect([[
+      ~                                                 |
+      ~                                                 |
+      [No Name]                                         |
+      :!printf foo; sleep 200                           |
+                                                        |
+      foo                                               |
+      -- TERMINAL --                                    |
+    ]])
+  end)
+end)