vim-patch:8.2.2632: not all command line arguments are tested

Problem:    Not all command line arguments are tested.
Solution:   Add tests for -D and -serverlist. (Dominique Pellé, closes vim/vim#7992)
c5cf369e95

Cherry-pick two deletions from patch 8.2.1799.

src/nvim/testdir/test_clientserver.vim

@@ -38,6 +38,14 @@ func Test_client_server()
   " When using valgrind it takes much longer.
   call WaitForAssert({-> assert_match(name, serverlist())})
 
+  if !has('win32')
+    if RunVim([], [], '--serverlist >Xtest_serverlist')
+      let lines = readfile('Xtest_serverlist')
+      call assert_true(index(lines, 'XVIMTEST') >= 0)
+    endif
+    call delete('Xtest_serverlist')
+  endif
+
   eval name->remote_foreground()
 
   call remote_send(name, ":let testvar = 'yes'\<CR>")

src/nvim/testdir/test_startup.vim

@@ -1130,7 +1130,6 @@ func Test_n_arg()
     call assert_equal([], readfile('Xtestout'))
     call delete('Xtestout')
   endif
-  call delete('Xafter')
 endfunc
 
 " Test for the "-h" (help) argument
@@ -1164,7 +1163,21 @@ func Test_E_arg()
     call assert_equal([], readfile('Xtestout'))
     call delete('Xtestout')
   endif
-  call delete('Xafter')
+endfunc
+
+" Test for the "-D" (debugger) argument
+func Test_D_arg()
+  CheckRunVimInTerminal
+
+  let cmd = GetVimCommandCleanTerm() .. ' -D'
+  let buf = term_start(cmd, {'term_rows' : 10})
+  call WaitForAssert({-> assert_equal("running", term_getstatus(buf))})
+
+  call WaitForAssert({-> assert_equal('Entering Debug mode.  Type "cont" to continue.',
+  \                  term_getline(buf, 7))})
+  call WaitForAssert({-> assert_equal('>', term_getline(buf, 10))})
+
+  call StopVimInTerminal(buf)
 endfunc
 
 " Test for too many edit argument errors