feature: provide configuration for locked id response value

config/test.exs

@@ -3,3 +3,5 @@ use Mix.Config
 config :ethereumex, url: "http://localhost:8545"
 
 config :ethereumex, ipc_path: "/.local/share/io.parity.ethereum/jsonrpc.ipc"
+
+# config :ethereumex, id_lock: "0"

lib/ethereumex/counter.ex

@@ -19,11 +19,30 @@ defmodule Ethereumex.Counter do
 
   @spec increment(atom()) :: integer()
   def increment(key) do
-    :ets.update_counter(@tab, key, {2, 1}, {key, 0})
+    do_increment(Application.get_env(:ethereumex, :id_lock), key)
   end
 
   @spec increment(atom(), integer()) :: integer()
   def increment(key, count) do
+    do_increment(Application.get_env(:ethereumex, :id_lock), key, count)
+  end
+
+  @spec do_increment(binary() | nil, atom()) :: integer()
+  defp do_increment(nil, key) do
+    :ets.update_counter(@tab, key, {2, 1}, {key, 0})
+  end
+
+  defp do_increment(id_lock, _key) do
+    id_lock
+  end
+
+  @spec do_increment(binary() | nil, atom(), integer()) :: integer()
+  defp do_increment(nil, key, count) do
     :ets.update_counter(@tab, key, {2, count}, {key, 0})
   end
+
+  @spec do_increment(binary() | nil, atom(), integer()) :: integer()
+  defp do_increment(id_lock, _key, _count) do
+    id_lock
+  end
 end

test/ethereumex/counter_lock_test.exs

@@ -0,0 +1,28 @@
+defmodule Ethereumex.CounterLockTest do
+  use ExUnit.Case
+  alias Ethereumex.Counter
+
+  setup do
+    Application.put_env(:ethereumex, :id_lock, "0")
+
+    on_exit(fn ->
+      Application.put_env(:ethereumex, :id_lock, nil)
+    end)
+  end
+
+  test "incrementing twice returns correct locked binary" do
+    "0" = Counter.increment(:test_1)
+    "0" = Counter.increment(:test_1)
+  end
+
+  test "incrementing twice and updating with a count returns correct locked binary" do
+    "0" = Counter.increment(:test_2)
+    "0" = Counter.increment(:test_2, 2)
+  end
+
+  test "incrementing twice, updating with a count and incrementing again returns correct locked binary" do
+    "0" = Counter.increment(:test_3)
+    "0" = Counter.increment(:test_3, 2)
+    "0" = Counter.increment(:test_3)
+  end
+end