T proxy() {
      return proxy;
    }
A trivial home-made mocking framework.

<p>Mockito 5 no longer supports Java 8, and we do, so rather than pinning to an older version
of Mockito we fake it with {@link Reflection}. This is only really possible because the thing
we want to mock ({@link SerializationStreamWriter}) is an interface. Furthermore all its
methods return void so we don't even need a way to specify what to return.

<p>The idea is that you make an instance of this class, have the code under test call methods
on it, then call {@link #verify} with a lambda that repeats the expected calls. If they match
the actual calls then the test passes.
value/src/it/functional/src/test/java/com/google/auto/value/gwt/CustomFieldSerializerTest.java