Improve specs on Upperkut::Configuration

spec/upperkut_spec.rb

@@ -11,16 +11,52 @@ def call(_worker, _items); end
       default = Upperkut::Configuration.default
 
       expect(default.polling_interval).to eq 5
+    end
+  end
+
+  describe '#server_middlewares' do
+    let(:config) { Upperkut::Configuration.default }
+
+    context 'when block is given' do
+      it 'yields the current server middlewares configuration and return it' do
+        config.server_middlewares do |chain|
+          expect(chain).to be_an(Upperkut::Middleware::Chain)
+          chain.add MyMiddleware
+        end
+        expect(config.server_middlewares.items).to eq([MyMiddleware])
+      end
+    end
 
-      default.server_middlewares do |chain|
-        chain.add MyMiddleware
+    context 'when no block is given' do
+      it 'returns memoized server middlewares with current configuration' do
+        server_middlewares = config.server_middlewares
+        expect(server_middlewares).to eq(config.server_middlewares)
+        expect(server_middlewares).to be_an(Upperkut::Middleware::Chain)
+        expect(server_middlewares.items).to eq([])
       end
+    end
+  end
+
+  describe '#client_middlewares' do
+    let(:config) { Upperkut::Configuration.default }
+
+    context 'when block is given' do
+      it 'yields the current client middlewares configuration and return it' do
+        config.client_middlewares do |chain|
+          expect(chain).to be_an(Upperkut::Middleware::Chain)
+          chain.add MyMiddleware
+        end
+        expect(config.client_middlewares.items).to eq([MyMiddleware])
+      end
+    end
 
-      default.client_middlewares do |chain|
-        chain.add MyMiddleware
+    context 'when no block is given' do
+      it 'returns memoized client middlewares with current configuration' do
+        client_middlewares = config.client_middlewares
+        expect(client_middlewares).to eq(config.client_middlewares)
+        expect(client_middlewares).to be_an(Upperkut::Middleware::Chain)
+        expect(client_middlewares.items).to eq([])
       end
-      expect(default.server_middlewares.items).to eq([MyMiddleware])
-      expect(default.client_middlewares.items).to eq([MyMiddleware])
     end
   end
 end