move redis_iterator test to its own file

test/test_api.rb

@@ -10,21 +10,6 @@ class TestApi < Sidekiq::Test
       Sidekiq.redis {|c| c.flushdb }
     end
 
-    describe '.sscan' do
-      include Sidekiq::RedisIterator
-      before do
-        50.times do |i|
-          Sidekiq.redis { |conn| conn.sadd('processes', "test-process-#{i}") }
-        end
-      end
-      it 'returns identical to smembers' do
-        sscan = Sidekiq.redis { |c| Sidekiq::Stats.new.sscan(c, 'processes') }.sort!
-        smembers = Sidekiq.redis { |c| c.smembers('processes') }.sort!
-        assert_equal sscan.size, 50
-        assert_equal sscan, smembers
-      end
-    end
-
     describe "stats" do
       it "is initially zero" do
         s = Sidekiq::Stats.new

test/test_redis_iterator.rb

@@ -0,0 +1,24 @@
+# frozen_string_literal: true
+require_relative 'helper'
+require 'sidekiq/redis_iterator'
+
+class TestRedisIterator < Sidekiq::Test
+
+  class Helper
+    include Sidekiq::RedisIterator
+  end
+
+  describe '.sscan' do
+    before do
+      50.times do |i|
+        Sidekiq.redis { |conn| conn.sadd('processes', "test-process-#{i}") }
+      end
+    end
+    it 'returns identical to smembers' do
+      sscan = Sidekiq.redis { |c| Helper.new.sscan(c, 'processes') }.sort!
+      smembers = Sidekiq.redis { |c| c.smembers('processes') }.sort!
+      assert_equal sscan.size, 50
+      assert_equal sscan, smembers
+    end
+  end
+end