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).