### Question:
DatarefExtension implements Extension { public URI getDataref() { return dataref; }  URI getDataref(); void setDataref(URI dataref); @Override void readFrom(CloudEventExtensions extensions); @Override Object getValue(String key); @Override Set<String> getKeys(); @Override String toString(); @Override int hashCode(); @Override boolean equals(Object obj); static final String DATAREF; }### Answer:
@Test public void parseExtension() { CloudEvent event = CloudEventBuilder.v1() .withId("aaa") .withSource(URI.create("http: .withType("example") .withExtension(DatarefExtension.DATAREF, "http: .build(); DatarefExtension datarefExtension = ExtensionProvider.getInstance() .parseExtension(DatarefExtension.class, event); assertThat(datarefExtension).isNotNull(); assertThat(datarefExtension.getDataref()).isEqualTo(URI.create("http: }