Nullery: self-aware nulls for testing

Nullery.java

public class Nullery {
  private static MockObjectNamingScheme namingScheme = new CamelCaseNamingScheme();

  private static Imposteriser imposteriser = ClassImposteriser.INSTANCE;

  public static <T> T nulled(Class<T> typeToNull) {
    return nulled(typeToNull, namingScheme.defaultNameFor(typeToNull));
  }

  public static <T> T nulled(Class<T> typeToMock, final String name) {
    Invokable invokable = new Invokable() {
      @Override
      public Object invoke(Invocation invocation) throws Throwable {
        NullPointerException npe = new NullPointerException(format("Called %s#%s", name, invocation.getInvokedMethod().getName()));
        StackTraceElement[] trace = npe.getStackTrace();
        npe.setStackTrace(Arrays.copyOfRange(trace, 3, trace.length));
        throw npe;
      }
    };
    return imposteriser.imposterise(invokable, typeToMock, CaptureControl.class);
  }
}

NulleryTest.java

interface Invokable {
  void invoke();
}

static class Invoker {
  Invokable invokable;

  Invoker(Invokable invokable) {
    this.invokable = invokable;
  }

  void process() {
    invokable.invoke();
  }
}

@Test
public void shouldThrowNpeWithGoodMessage() {
  Invokable nullInvokable = Nullery.nulled(Invokable.class);
  Invoker invoker = new Invoker(nullInvokable);
  try {
    invoker.process();
    fail("Expected a NPE");
  } catch (NullPointerException npe) {
    npe.printStackTrace();
    assertThat(npe.getMessage(), Matchers.containsString("invokable#invoke"));
  }
}