patch 8.2.0316: ex_getln.c code has insufficient test coverage

Problem:    ex_getln.c code has insufficient test coverage.
Solution:   Add more tests. Fix a problem. (Yegappan Lakshmanan, closes #5693)

src/testdir/test_functions.vim

@@ -1141,6 +1141,30 @@ func Test_col()
   bw!
 endfunc
 
+" Test for input()
+func Test_input_func()
+  " Test for prompt with multiple lines
+  redir => v
+  call feedkeys(":let c = input(\"A\\nB\\nC\\n? \")\<CR>B\<CR>", 'xt')
+  redir END
+  call assert_equal("B", c)
+  call assert_equal(['A', 'B', 'C'], split(v, "\n"))
+
+  " Test for default value
+  call feedkeys(":let c = input('color? ', 'red')\<CR>\<CR>", 'xt')
+  call assert_equal('red', c)
+
+  " Test for completion at the input prompt
+  func! Tcomplete(arglead, cmdline, pos)
+    return "item1\nitem2\nitem3"
+  endfunc
+  call feedkeys(":let c = input('Q? ', '' , 'custom,Tcomplete')\<CR>"
+        \ .. "\<C-A>\<CR>", 'xt')
+  delfunc Tcomplete
+  call assert_equal('item1 item2 item3', c)
+endfunc
+
+" Test for inputlist()
 func Test_inputlist()
   call feedkeys(":let c = inputlist(['Select color:', '1. red', '2. green', '3. blue'])\<cr>1\<cr>", 'tx')
   call assert_equal(1, c)
@@ -2034,3 +2058,5 @@ func Test_echoraw()
   call StopVimInTerminal(buf)
   call delete('XTest_echoraw')
 endfunc
+
+" vim: shiftwidth=2 sts=2 expandtab