Write a unit test for downloading a file

Question

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: ``` 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; public void setBill(List userBillings) { this.userBillings = userBillings; } public void download(HttpServletResponse response, String reportType) { response.setContentType("application/vnd.ms-excel"); response.setHeader("Content-Disposition", "attachment;…

Accepted Answer

When you create a mock object

```
mockResponse = mock(HttpServletResponse.class);
```

by default, all its methods that have a reference type return type (minus a few special cases) return `null`.

So the return value of `getOutputStream()` in this snippet

```
ServletOutputStream outputStream = response.getOutputStream();
```

is `null`.

You need to set expectations and specify a return value.

```
when(mockResponse.getOutputStream().thenReturn(/* the value to return when that method is invoked */);
```

This is called stubbing.

Write a unit test for downloading a file

Solution

Problem