how to throw IOException while reading a file using Mockito?

Question

I have to throw an IOException using Mockito for a method, which is reading an input stream like given below. Is there any way to do it?

public void someMethod(){
 try{
  BufferedReader in = new BufferedReader(new InputStreamReader(inputStream));
  firstLine = in.readLine();
 }catch(IOException ioException){
  //Do something
 }

I tried mocking like

  BufferedReader buffReader = Mockito.mock(BufferedReader.class);
  Mockito.doThrow(new IOException()).when(buffReader).readLine();

but didn't work out :(

Answer 1

You're mocking a BufferedReader, but your method doesn't use your mock. It uses its own, new BufferedReader. You need to be able to inject your mock into the method.

It seems that inputStream is a field of the class containing this method. So you could mock the inputStream instead and make it throw an IOException when its read() method is called (by the InputStreamReader).