### Question:
DocumentFile { public String getInvariantStream() { return invariantStream; } private  DocumentFile(); static org.oulipo.streams.Compiler<DocumentFile> compiler(); static Decompiler<DocumentFile> decompiler(); Map<Integer, String> get(); String getDocumentHash(); String getEncyptedInvariantStream(); String getGenesisHash(); String getHashPreviousBlock(); String getInvariantStream(); int getMajorVersion(); int getMinorVersion(); List<Op> getOps(); Overlay getOverlay(int overlayIndex); Map<Integer, Overlay> getOverlayPool(); Set<Overlay> getOverlays(Set<Integer> indicies); String getString(int stringPoolIndex); long getTimestamp(); boolean hasEncryptedInvariantStream(); boolean hasGenesisHash(); boolean hasHashPreviousBlock(); boolean hasInvariantStream(); int operationCount(); int overlayPoolSize(); int stringPoolSize(); static final byte[] MAGIC; }### Answer:
@Test public void addText() throws Exception { DocumentFile.Builder builder = new DocumentFile.Builder("fakeHash"); builder.appendText("Xanadu"); builder.appendText("Green"); DocumentFile file = builder.build(); assertEquals("XanaduGreen", file.getInvariantStream()); }