@Override
  protected InputStream readInputStreamParam(String key) {
    Part part = readPart(key);
    return (part == null) ? null : part.getInputStream();
  }
@Test
  public void read_input_stream() throws Exception {
    when(source.getContentType()).thenReturn("multipart/form-data");
    InputStream file = mock(InputStream.class);
    Part part = mock(Part.class);
    when(part.getInputStream()).thenReturn(file);
    when(part.getSize()).thenReturn(10L);
    when(source.getPart("param1")).thenReturn(part);

    assertThat(underTest.readInputStreamParam("param1")).isEqualTo(file);
    assertThat(underTest.readInputStreamParam("param2")).isNull();
  }