legacy tests: migrate test_qf_title

src/nvim/testdir/test_qf_title.in

@@ -1,18 +0,0 @@
-Tests for quickfix window's title     vim: set ft=vim :
-
-STARTTEST
-:so small.vim
-:if !has('quickfix') | e! test.ok | wq! test.out | endif
-:set efm=%E%f:%l:%c:%m
-:cgetexpr ['file:1:1:message']
-:let qflist=getqflist()
-:call setqflist(qflist, 'r')
-:copen
-:let g:quickfix_title=w:quickfix_title
-:wincmd p
-:$put =g:quickfix_title
-:/^Results/,$w test.out
-:qa!
-ENDTEST
-
-Results of test_qf_title:

src/nvim/testdir/test_qf_title.ok

@@ -1,2 +0,0 @@
-Results of test_qf_title:
-:setqflist()

test/functional/legacy/qf_title_spec.lua

@@ -0,0 +1,30 @@
+-- Tests for quickfix window's title
+
+local helpers = require('test.functional.helpers')
+local feed, insert, source = helpers.feed, helpers.insert, helpers.source
+local clear, execute, expect = helpers.clear, helpers.execute, helpers.expect
+
+describe('qf_title', function()
+  setup(clear)
+
+  it('is working', function()
+    insert([[
+      Results of test_qf_title:]])
+
+    source([[
+      set efm=%E%f:%l:%c:%m
+      cgetexpr ['file:1:1:message']
+      let qflist=getqflist()
+      call setqflist(qflist, 'r')
+      copen
+      let g:quickfix_title=w:quickfix_title
+      wincmd p
+      $put =g:quickfix_title
+    ]])
+
+    -- Assert buffer contents.
+    expect([[
+      Results of test_qf_title:
+      :setqflist()]])
+  end)
+end)