@Override
              public Void answer(InvocationOnMock invocation) throws Throwable {
                Integer alpha = (Integer) invocation.getArguments()[0];
                drawable.invalidateSelf();
                atomicInteger.set(alpha);
                return null;
              }
Stubs setAlpha method.

@param drawable to stub method of
drawee/src/test/java/com/facebook/drawee/drawable/DrawableTestUtils.java