Add tests for configuration API.

test/test_config.rb

@@ -0,0 +1,21 @@
+require_relative 'helper'
+
+class TestConfig < MiniTest::Unit::TestCase
+  def setup
+    @saved = Sidetiq.config
+    Sidetiq.config = OpenStruct.new
+  end
+
+  def teardown
+    Sidetiq.config = @saved
+  end
+
+  def test_configure
+    Sidetiq.configure do |config|
+      config.test = 42
+    end
+
+    assert_equal 42, Sidetiq.config.test
+  end
+end
+