vim-patch:8.2.0952: no simple way to interrupt Vim

Problem:    No simple way to interrupt Vim.
Solution:   Add the SigUSR1 autocommand, triggered by SIGUSR1. (Jacob Hayes,
            closes vim/vim#1718)
be5ee8686a

src/nvim/testdir/test_autocmd.vim

@@ -1897,4 +1897,17 @@ func Test_autocmd_FileReadCmd()
   delfunc ReadFileCmd
 endfunc
 
+" Tests for SigUSR1 autocmd event, which is only available on posix systems.
+func Test_autocmd_sigusr1()
+  CheckUnix
+
+  let g:sigusr1_passed = 0
+  au Signal SIGUSR1 let g:sigusr1_passed = 1
+  call system('/bin/kill -s usr1 ' . getpid())
+  call WaitForAssert({-> assert_true(g:sigusr1_passed)})
+
+  au! Signal
+  unlet g:sigusr1_passed
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab