patch 8.2.4597: LuaV_debug() not covered by tests

Problem:    LuaV_debug() not covered by tests.
Solution:   Add a test. (Dominique Pellé, closes #9980)
diff --git a/src/testdir/test_lua.vim b/src/testdir/test_lua.vim
index fd265ef..1f2df10 100644
--- a/src/testdir/test_lua.vim
+++ b/src/testdir/test_lua.vim
@@ -1192,4 +1192,27 @@
   augroup! Luagroup
 endfunc
 
+func Test_lua_debug()
+  CheckRunVimInTerminal
+
+  let buf = RunVimInTerminal('', {'rows': 10})
+  call term_sendkeys(buf, ":lua debug.debug()\n")
+  call WaitForAssert({-> assert_equal('lua_debug> ', term_getline(buf, 10))})
+
+  call term_sendkeys(buf, "foo = 42\n")
+  call WaitForAssert({-> assert_equal('lua_debug> foo = 42', term_getline(buf, 9))})
+  call WaitForAssert({-> assert_equal('lua_debug> ',         term_getline(buf, 10))})
+
+  call term_sendkeys(buf, "print(foo)\n")
+  call WaitForAssert({-> assert_equal('lua_debug> print(foo)', term_getline(buf, 8))})
+  call WaitForAssert({-> assert_equal('42',                    term_getline(buf, 9))})
+  call WaitForAssert({-> assert_equal('lua_debug> ',           term_getline(buf, 10))})
+
+  call term_sendkeys(buf, "cont\n")
+  call WaitForAssert({-> assert_match(' All$', term_getline(buf, 10))})
+
+  call StopVimInTerminal(buf)
+  call delete('XtestLuaDebug.vim')
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab