### Question:
InstalledExtensionDocumentTree { public Set<DocumentReference> getChildren(EntityReference parentReference) { InstalledExtensionDocumentTreeNode parentNode = this.nodes.get(parentReference); return parentNode == null ? Collections.emptySet() : parentNode.children; }  Set<DocumentReference> getChildren(EntityReference parentReference); boolean isExtensionPage(DocumentReference documentReference); boolean isCustomizedExtensionPage(DocumentReference documentReference); Set<DocumentReference> getNestedExtensionPages(EntityReference rootReference); Set<DocumentReference> getNestedCustomizedExtensionPages(EntityReference rootReference);  }### Answer:
@Test public void getChildren() { assertEquals(Collections.singleton(this.path), this.tree.getChildren(this.alice.getWikiReference())); assertEquals(new HashSet<>(Arrays.asList(this.to, this.bob)), this.tree.getChildren(path)); assertEquals(Collections.singleton(alice), this.tree.getChildren(this.to)); assertEquals(Collections.emptySet(), this.tree.getChildren(alice)); assertEquals(Collections.emptySet(), this.tree.getChildren(bob)); assertEquals(new HashSet<>(Arrays.asList(this.carol, this.users)), this.tree.getChildren(carol.getWikiReference())); assertEquals(Collections.singleton(this.john), this.tree.getChildren(carol)); assertEquals(Collections.singleton(this.denis), this.tree.getChildren(users)); assertEquals(Collections.emptySet(), this.tree.getChildren(denis)); assertEquals(Collections.emptySet(), this.tree.getChildren(new WikiReference("test"))); assertEquals(Collections.emptySet(), this.tree.getChildren(this.bob.getLastSpaceReference())); assertEquals(Collections.emptySet(), this.tree.getChildren(new DocumentReference("bar", Arrays.asList("Carol", "John"), "WebHome"))); assertEquals(Collections.emptySet(), this.tree.getChildren(new DocumentReference(this.path, Locale.FRENCH))); }