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Testing Metrics Stream Servlet Shutdown Behavior in Netflix Hystrix

This test suite validates the functionality of the HystrixMetricsStreamServlet, a crucial component in Netflix’s Hystrix library that handles metric event streaming. The tests focus on servlet lifecycle management and request handling, particularly during shutdown scenarios.

Test Coverage Overview

The test suite provides targeted coverage of the HystrixMetricsStreamServlet’s shutdown behavior and request handling.

Key areas tested include:

Servlet initialization and destruction
Request rejection during shutdown state
HTTP response handling
Metric stream management

Implementation Analysis

The testing approach utilizes Mockito for dependency isolation and JUnit for test structure.

Notable patterns include:

Mock injection for HTTP servlet components
RxJava Observable simulation for metric streams
Lifecycle method verification
Error response validation

Technical Details

Testing infrastructure includes:

JUnit 4 test framework
Mockito mocking framework
RxJava for reactive stream testing
Mock objects for HttpServletRequest, HttpServletResponse, and PrintWriter
Custom DashboardData stream simulation

Best Practices Demonstrated

The test suite exemplifies several testing best practices:

Proper test setup and teardown management
Isolation of external dependencies
Clear test method naming conventions
Focused test scenarios
Explicit verification of expected behaviors

netflix/hystrix

hystrix-contrib/hystrix-metrics-event-stream/src/test/java/com/netflix/hystrix/contrib/metrics/eventstream/HystrixMetricsStreamServletUnitTest.java

            
/**
 * Copyright 2015 Netflix, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.netflix.hystrix.contrib.metrics.eventstream;

import com.netflix.hystrix.metric.consumer.HystrixDashboardStream;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;
import org.mockito.Mock;
import org.mockito.MockitoAnnotations;
import rx.Observable;
import rx.functions.Func1;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.concurrent.TimeUnit;

import static org.mockito.Mockito.mock;
import static org.mockito.Mockito.verify;
import static org.mockito.Mockito.when;

public class HystrixMetricsStreamServletUnitTest {

    @Mock HttpServletRequest mockReq;
    @Mock HttpServletResponse mockResp;
    @Mock HystrixDashboardStream.DashboardData mockDashboard;
    @Mock PrintWriter mockPrintWriter;

    HystrixMetricsStreamServlet servlet;

    private final Observable<HystrixDashboardStream.DashboardData> streamOfOnNexts =
            Observable.interval(100, TimeUnit.MILLISECONDS).map(new Func1<Long, HystrixDashboardStream.DashboardData>() {
                @Override
                public HystrixDashboardStream.DashboardData call(Long timestamp) {
                    return mockDashboard;
                }
            });


    @Before
    public void init() {
        MockitoAnnotations.initMocks(this);
        when(mockReq.getMethod()).thenReturn("GET");
    }

    @After
    public void tearDown() {
        servlet.destroy();
        servlet.shutdown();
    }

    @Test
    public void shutdownServletShouldRejectRequests() throws ServletException, IOException {
        servlet = new HystrixMetricsStreamServlet(streamOfOnNexts, 10);
        try {
            servlet.init();
        } catch (ServletException ex) {

        }

        servlet.shutdown();

        servlet.service(mockReq, mockResp);

        verify(mockResp).sendError(503, "Service has been shut down.");
    }
}