@Test
  public void removeCallback() {
    surfaceHolder.addCallback(callback1);
    surfaceHolder.addCallback(callback2);

    assertThat(fakeSurfaceHolder.getCallbacks().size()).isEqualTo(2);

    surfaceHolder.removeCallback(callback1);

    assertThat(fakeSurfaceHolder.getCallbacks()).doesNotContain(callback1);
    assertThat(fakeSurfaceHolder.getCallbacks()).contains(callback2);
  }
  @Test
  public void addCallback() {
    assertThat(fakeSurfaceHolder.getCallbacks()).isEmpty();

    surfaceHolder.addCallback(callback1);

    assertThat(fakeSurfaceHolder.getCallbacks()).contains(callback1);

    surfaceHolder.addCallback(callback2);

    assertThat(fakeSurfaceHolder.getCallbacks()).contains(callback1);
    assertThat(fakeSurfaceHolder.getCallbacks()).contains(callback2);
  }