Added unit test for books getChildren() method (#6602)

* started unit tests for books

* added first unit test for getchildren()

* fixed dependencies and use tmpdir

* latest from master

extensions/notebook/src/book/bookTreeItem.ts

@@ -100,6 +100,14 @@ export class BookTreeItem extends vscode.TreeItem {
 		}
 	}
 
+	public get title(): string {
+		return this.book.title;
+	}
+
+	public get uri(): string {
+		return this._uri;
+	}
+
 	public get root(): string {
 		return this.book.root;
 	}
@@ -128,4 +136,4 @@ export class BookTreeItem extends vscode.TreeItem {
 			return undefined;
 		}
 	}
-}
+}