Statistics test: guarantee empty members then assert is_nil for first_join_year

test/mv/statistics_test.exs

@@ -7,6 +7,7 @@ defmodule Mv.StatisticsTest do
   require Ash.Query
   import Ash.Expr
 
+  alias Mv.Membership.Member
   alias Mv.Statistics
   alias Mv.MembershipFees
   alias Mv.MembershipFees.MembershipFeeCycle
@@ -46,9 +47,13 @@ defmodule Mv.StatisticsTest do
     end
 
     test "returns nil when no members exist", %{actor: actor} do
-      # Expects empty member table (sandbox isolation). If flaky, ensure no other test creates members.
+      # Guarantee empty member table so the assertion is deterministic
+      Member
+      |> Ash.read!(actor: actor)
+      |> Enum.each(&Ash.destroy!(&1, actor: actor))
+
       result = Statistics.first_join_year(actor: actor)
-      assert result == nil
+      assert is_nil(result)
     end
   end