tests: Add more coverage for table.concat corner cases

tests/conformance/tables.lua

@@ -412,6 +412,25 @@ do
   assert(table.find({[(1)] = true}, true) == 1)
 end
 
+-- test table.concat
+do
+  -- hash elements
+  local t = {}
+  t[123] = "a"
+  t[124] = "b"
+
+  assert(table.concat(t) == "")
+  assert(table.concat(t, ",", 123, 124) == "a,b")
+  assert(table.concat(t, ",", 123, 123) == "a")
+
+  -- numeric values
+  assert(table.concat({1, 2, 3}, ",") == "1,2,3")
+  assert(table.concat({"a", 2, "c"}, ",") == "a,2,c")
+
+  -- out of bounds indices => element is nil => error
+  assert(pcall(table.concat, t, ",", 1, 100) == false)
+end
+
 -- test indexing with strings that have zeroes embedded in them
 do
 	local t = {}