vim-patch:8.1.1212: signal PWR is not tested

Problem:    Signal PWR is not tested.
Solution:   Test that PWR updates the swap file. (Dominique Pelle,
            closes vim/vim#4312)
520e245237

src/nvim/testdir/test_signals.vim

@@ -4,19 +4,18 @@ if !has('unix')
   finish
 endif
 
-if has('gui_running')
-  " Signals only work for terminals, and won't work for GUI.
-  finish
-endif
-
 source shared.vim
 
+" Check whether a signal is available on this system.
+func HasSignal(signal)
+  let signals = system('kill -l')
+  return signals =~# '\<' .. a:signal .. '\>'
+endfunc
+
 " Test signal WINCH (window resize signal)
 func Test_signal_WINCH()
   throw 'skipped: Nvim cannot avoid terminal resize'
-  let signals = system('kill -l')
-  if signals !~ '\<WINCH\>'
-    " signal WINCH is not available, skip the test.
+  if has('gui_running') || !HasSignal('WINCH')
     return
   endif
 
@@ -32,15 +31,15 @@ func Test_signal_WINCH()
   let new_lines = &lines - 2
   let new_columns = &columns - 2
 
-  exe 'set lines=' . new_lines
-  exe 'set columns=' . new_columns
+  exe 'set lines=' .. new_lines
+  exe 'set columns=' .. new_columns
   call assert_equal(new_lines, &lines)
   call assert_equal(new_columns, &columns)
 
   " Send signal and wait for signal to be processed.
   " 'lines' and 'columns' should have been restored
   " after handing signal WINCH.
-  exe 'silent !kill -s WINCH ' . getpid()
+  exe 'silent !kill -s WINCH ' .. getpid()
   call WaitForAssert({-> assert_equal(old_lines, &lines)})
   call assert_equal(old_columns, &columns)
 
@@ -48,3 +47,32 @@ func Test_signal_WINCH()
     let &t_WS = old_WS
   endif
 endfunc
+
+" Test signal PWR, which should update the swap file.
+func Test_signal_PWR()
+  if !HasSignal('PWR')
+    return
+  endif
+
+  " Set a very large 'updatetime' and 'updatecount', so that we can be sure
+  " that swap file is updated as a result of sending PWR signal, and not
+  " because of exceeding 'updatetime' or 'updatecount' when changing buffer.
+  set updatetime=100000 updatecount=100000
+  new Xtest_signal_PWR
+  let swap_name = swapname('%')
+  call setline(1, '123')
+  preserve
+  let swap_content = readfile(swap_name, 'b')
+
+  " Update the buffer and check that the swap file is not yet updated,
+  " since we set 'updatetime' and 'updatecount' to large values.
+  call setline(1, 'abc')
+  call assert_equal(swap_content, readfile(swap_name, 'b'))
+
+  " Sending PWR signal should update the swap file.
+  exe 'silent !kill -s PWR ' .. getpid()
+  call WaitForAssert({-> assert_notequal(swap_content, readfile(swap_name, 'b'))})
+
+  bwipe!
+  set updatetime& updatecount&
+endfunc