Java 编写一个下载文件的单元测试
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Write a unit test for downloading a file
提问by pezetem
At the moment I wrote a small downloadService which let's user download a file (at the moment only excel). The code works properly, however I do not know how to write the unit test for it. That's my code:
目前我写了一个小的 downloadService 让我们用户下载一个文件（目前只有 excel）。代码工作正常，但是我不知道如何为它编写单元测试。那是我的代码：
package com.pzm.service;
import com.pzm.model.UserBillingsMock;
import com.pzm.model.report.ExcelReport;
import com.pzm.model.report.Report;
import com.pzm.model.report.ReportFactory;
import org.springframework.stereotype.Repository;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.util.List;
/**
* Created by akfaz on 6/26/14.
*/
@Repository
public class DownloadService {
private Report report;
private List<UserBillings> userBillings;
public void setBill(List<UserBillings> userBillings) {
this.userBillings = userBillings;
}
public void download(HttpServletResponse response, String reportType) {
response.setContentType("application/vnd.ms-excel");
response.setHeader("Content-Disposition", "attachment; filename=MyExcel.xls");
report = new ReportFactory().create(reportType, userBillings);
saveFile(response, report);
}
private void saveFile(HttpServletResponse response, Report report) {
try {
ServletOutputStream outputStream = response.getOutputStream();
report.write(outputStream);
outputStream.flush();
} catch (IOException e) {
e.printStackTrace();
}
}
}
the unit test - tried to use Mockito, but got the exception:
单元测试 - 尝试使用 Mockito，但出现异常：
unit test:
单元测试：
package com.pzm.service;
import junit.framework.TestCase;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;
import javax.servlet.http.HttpServletResponse;
import static org.mockito.Mockito.*;
/**
* Created by akfaz on 7/5/14.
*/
public class DownloadServiceTest extends TestCase{
HttpServletResponse mockResponse;
DownloadService downloadService;
@Before
public void setUp() throws Exception {
mockResponse = mock(HttpServletResponse.class);
downloadService = new DownloadService();
}
@Test
public void testDownload() throws Exception {
downloadService.download(mockResponse, "xls");
verify(mockResponse).getContentType();
}
}
and the exception:
和例外：
org.apache.poi.openxml4j.exceptions.OpenXML4JRuntimeException: Fail to save: an error occurs while saving the package : null
at org.apache.poi.openxml4j.opc.ZipPackage.saveImpl(ZipPackage.java:500)
at org.apache.poi.openxml4j.opc.OPCPackage.save(OPCPackage.java:1417)
at org.apache.poi.POIXMLDocument.write(POIXMLDocument.java:179)
at com.pzm.model.report.ExcelReport.write(ExcelReport.java:46)
at com.pzm.service.DownloadService.saveFile(DownloadService.java:40)
at com.pzm.service.DownloadService.download(DownloadService.java:34)
at com.pzm.service.DownloadServiceTest.testDownload(DownloadServiceTest.java:32)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at org.junit.internal.runners.JUnit38ClassRunner.run(JUnit38ClassRunner.java:83)
at org.junit.runner.JUnitCore.run(JUnitCore.java:157)
at com.intellij.junit4.JUnit4IdeaTestRunner.startRunnerWithArgs(JUnit4IdeaTestRunner.java:74)
at com.intellij.rt.execution.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:202)
at com.intellij.rt.execution.junit.JUnitStarter.main(JUnitStarter.java:65)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at com.intellij.rt.execution.application.AppMain.main(AppMain.java:120)
Caused by: java.lang.NullPointerException
at java.util.zip.DeflaterOutputStream.<init>(DeflaterOutputStream.java:84)
at java.util.zip.DeflaterOutputStream.<init>(DeflaterOutputStream.java:142)
at java.util.zip.ZipOutputStream.<init>(ZipOutputStream.java:118)
at java.util.zip.ZipOutputStream.<init>(ZipOutputStream.java:104)
at org.apache.poi.openxml4j.opc.ZipPackage.saveImpl(ZipPackage.java:433)
... 28 more
采纳答案by Sotirios Delimanolis
When you create a mock object
创建模拟对象时
mockResponse = mock(HttpServletResponse.class);
by default, all its methods that have a reference type return type (minus a few special cases) return null.
默认情况下，其所有具有引用类型的方法都返回类型（减去一些特殊情况） return null。
So the return value of getOutputStream()in this snippet
所以getOutputStream()这个片段中的返回值
ServletOutputStream outputStream = response.getOutputStream();
is null.
是null。
You need to set expectations and specify a return value.
您需要设置期望值并指定返回值。
when(mockResponse.getOutputStream().thenReturn(/* the value to return when that method is invoked */);
This is called stubbing.
这称为存根。
