public <T extends AbstractConfig> void setConfigValueMapper(final Class<T> clazz,
                                                                final UnaryOperator<T> valueMapper) {
        configMapperSpy.setConfigValueMapper(clazz, valueMapper);
    }
Sets a single config value mapper that allows you to change the config value from its
defaults. Multiple call to this for the same class will override previous calls for that
class.
stroom-app/src/test/java/stroom/test/AbstractStatisticsCoreIntegrationTest.java