### Question:
PrefixingConfigurationSourceWrapper implements ConfigurationSource { @Override public String getValue(String key) { return delegate.getValue(prefix + key); } PrefixingConfigurationSourceWrapper(ConfigurationSource delegate, String prefix); @Override String getValue(String key); @Override void reload(); @Override String getName(); @Override boolean isSavingPossible(); @Override boolean isSavingPersistent(); @Override void save(String key, String value);  }### Answer:
@Test void getValue() { System.setProperty("elastic.apm.foo", "bar"); assertThat(sourceWrapper.getValue("foo")).isEqualTo("bar"); }