feat: add flag threshold test

examples/gno.land/r/demo/boards2/z_2_a_filetest.gno

@@ -16,7 +16,7 @@ func main() {
 	bid := boards2.CreateBoard("test1")
 	pid := boards2.CreateThread(bid, "thread", "thread")
 	boards2.FlagThread(bid, pid, "reason")
-	rid := boards2.CreateReply(bid, pid, pid, "reply")
+	_ = boards2.CreateReply(bid, pid, pid, "reply")
 }
 
 // Error:

examples/gno.land/r/demo/boards2/z_2_d_filetest.gno

@@ -0,0 +1,25 @@
+package main
+
+import (
+	"std"
+
+	"gno.land/r/demo/boards2"
+)
+
+const owner = std.Address("g1jg8mtutu9khhfwc4nxmuhcpftf0pajdhfvsqf5") // @test1
+
+func init() {
+	std.TestSetOrigCaller(owner)
+}
+
+func main() {
+	// Only single user per flag can't be tested atm, as flagThreshold = 1.
+	bid := boards2.CreateBoard("test1")
+	pid := boards2.CreateThread(bid, "thread", "thread")
+
+	boards2.FlagThread(bid, pid, "reason1")
+	boards2.FlagThread(bid, pid, "reason2")
+}
+
+// Error:
+// item flag count threshold exceeded: 1