diff --git a/extensions/notebook/src/book/bookTreeView.ts b/extensions/notebook/src/book/bookTreeView.ts
index fc5f48d130..5d5137f00a 100644
--- a/extensions/notebook/src/book/bookTreeView.ts
+++ b/extensions/notebook/src/book/bookTreeView.ts
@@ -28,6 +28,8 @@ export class BookTreeViewProvider implements vscode.TreeDataProvider<BookTreeIte
 	private _extensionContext: vscode.ExtensionContext;
 	private _throttleTimer: any;
 	private _resource: string;
+	// For testing
+	private _errorMessage: string;
 	private _onReadAllTOCFiles: vscode.EventEmitter<void> = new vscode.EventEmitter<void>();
 	private _openAsUntitled: boolean;
 
@@ -194,8 +196,12 @@ export class BookTreeViewProvider implements vscode.TreeDataProvider<BookTreeIte
 		}
 	}
 
-	private flattenArray(array: any[]): any[] {
-		return array.reduce((acc, val) => Array.isArray(val.sections) ? acc.concat(val).concat(this.flattenArray(val.sections)) : acc.concat(val), []);
+	private flattenArray(array: any[], title: string): any[] {
+		try {
+			return array.reduce((acc, val) => Array.isArray(val.sections) ? acc.concat(val).concat(this.flattenArray(val.sections, title)) : acc.concat(val), []);
+		} catch (e) {
+			throw localize('Invalid toc.yml', 'Error: {0} has an incorrect toc.yml file', title);
+		}
 	}
 
 	public getBooks(): BookTreeItem[] {
@@ -208,7 +214,7 @@ export class BookTreeViewProvider implements vscode.TreeDataProvider<BookTreeIte
 				let book = new BookTreeItem({
 					title: config.title,
 					root: root,
-					tableOfContents: this.flattenArray(tableOfContents),
+					tableOfContents: this.flattenArray(tableOfContents, config.title),
 					page: tableOfContents,
 					type: BookTreeItemType.Book,
 					treeItemCollapsibleState: vscode.TreeItemCollapsibleState.Expanded,
@@ -220,15 +226,15 @@ export class BookTreeViewProvider implements vscode.TreeDataProvider<BookTreeIte
 				);
 				books.push(book);
 			} catch (e) {
-				vscode.window.showErrorMessage(localize('openConfigFileError', "Open file {0} failed: {1}",
-					path.join(root, '_config.yml'),
-					e instanceof Error ? e.message : e));
+				let error = e instanceof Error ? e.message : e;
+				this._errorMessage = error;
+				vscode.window.showErrorMessage(error);
 			}
 		}
 		return books;
 	}
 
-	private getSections(tableOfContents: any[], sections: any[], root: string): BookTreeItem[] {
+	public getSections(tableOfContents: any[], sections: any[], root: string): BookTreeItem[] {
 		let notebooks: BookTreeItem[] = [];
 		for (let i = 0; i < sections.length; i++) {
 			if (sections[i].url) {
@@ -288,7 +294,9 @@ export class BookTreeViewProvider implements vscode.TreeDataProvider<BookTreeIte
 						);
 						notebooks.push(markdown);
 					} else {
-						vscode.window.showErrorMessage(localize('missingFileError', "Missing file : {0}", sections[i].title));
+						let error = localize('missingFileError', 'Missing file : {0}', sections[i].title);
+						this._errorMessage = error;
+						vscode.window.showErrorMessage(error);
 					}
 				}
 			} else {
@@ -317,6 +325,13 @@ export class BookTreeViewProvider implements vscode.TreeDataProvider<BookTreeIte
 		return Promise.resolve(result);
 	}
 
+	public get errorMessage() {
+		return this._errorMessage;
+	}
+
+	public get tableOfContentPaths() {
+		return this._tableOfContentPaths;
+	}
 	getUntitledNotebookUri(resource: string): vscode.Uri {
 		let title = this.findNextUntitledFileName(resource);
 		let untitledFileName: vscode.Uri = vscode.Uri.parse(`untitled:${title}`);
diff --git a/extensions/notebook/src/test/book/book.test.ts b/extensions/notebook/src/test/book/book.test.ts
index 0b9188fbbf..34c67cab70 100644
--- a/extensions/notebook/src/test/book/book.test.ts
+++ b/extensions/notebook/src/test/book/book.test.ts
@@ -154,3 +154,144 @@ describe('BookTreeViewProvider.getChildren', function (): void {
 		console.log('Successfully removed temporary files.');
 	});
 });
+
+describe('BookTreeViewProvider.getTableOfContentFiles', function (): void {
+	let rootFolderPath: string;
+	let tableOfContentsFile: string;
+	let bookTreeViewProvider: BookTreeViewProvider;
+	let folder: vscode.WorkspaceFolder;
+
+	this.beforeAll(async () => {
+		rootFolderPath = path.join(os.tmpdir(), `BookTestData_${uuid.v4()}`);
+		let dataFolderPath = path.join(rootFolderPath, '_data');
+		tableOfContentsFile = path.join(dataFolderPath, 'toc.yml');
+		let tableOfContentsFileIgnore = path.join(rootFolderPath, 'toc.yml');
+		await fs.mkdir(rootFolderPath);
+		await fs.mkdir(dataFolderPath);
+		await fs.writeFile(tableOfContentsFile, '');
+		await fs.writeFile(tableOfContentsFileIgnore, '');
+		let mockExtensionContext = TypeMoq.Mock.ofType<vscode.ExtensionContext>();
+		folder = {
+			uri: vscode.Uri.file(rootFolderPath),
+			name: '',
+			index: 0
+		};
+		bookTreeViewProvider = new BookTreeViewProvider([folder], mockExtensionContext.object);
+		let tocRead = new Promise((resolve, reject) => bookTreeViewProvider.onReadAllTOCFiles(() => resolve()));
+		let errorCase = new Promise((resolve, reject) => setTimeout(() => resolve(), 5000));
+		await Promise.race([tocRead, errorCase.then(() => { throw new Error('Table of Contents were not ready in time'); })]);
+	});
+
+	it('should ignore toc.yml files not in _data folder', function(): void {
+		bookTreeViewProvider.getTableOfContentFiles([folder.uri.toString()]);
+		for (let p of bookTreeViewProvider.tableOfContentPaths) {
+			should(p.toLocaleLowerCase()).equal(tableOfContentsFile.replace(/\\/g, '/').toLocaleLowerCase());
+		}
+	});
+
+	this.afterAll(async function () {
+		if (fs.existsSync(rootFolderPath)) {
+			rimraf.sync(rootFolderPath);
+		}
+	});
+});
+
+
+describe('BookTreeViewProvider.getBooks', function (): void {
+	let rootFolderPath: string;
+	let configFile: string;
+	let folder: vscode.WorkspaceFolder;
+	let bookTreeViewProvider: BookTreeViewProvider;
+	let mockExtensionContext: TypeMoq.IMock<vscode.ExtensionContext>;
+
+	this.beforeAll(async () => {
+		rootFolderPath = path.join(os.tmpdir(), `BookTestData_${uuid.v4()}`);
+		let dataFolderPath = path.join(rootFolderPath, '_data');
+		configFile = path.join(rootFolderPath, '_config.yml');
+		let tableOfContentsFile = path.join(dataFolderPath, 'toc.yml');
+		await fs.mkdir(rootFolderPath);
+		await fs.mkdir(dataFolderPath);
+		await fs.writeFile(tableOfContentsFile, 'title: Test');
+		mockExtensionContext = TypeMoq.Mock.ofType<vscode.ExtensionContext>();
+		folder = {
+			uri: vscode.Uri.file(rootFolderPath),
+			name: '',
+			index: 0
+		};
+		bookTreeViewProvider = new BookTreeViewProvider([folder], mockExtensionContext.object);
+		let tocRead = new Promise((resolve, reject) => bookTreeViewProvider.onReadAllTOCFiles(() => resolve()));
+		let errorCase = new Promise((resolve, reject) => setTimeout(() => resolve(), 5000));
+		await Promise.race([tocRead, errorCase.then(() => { throw new Error('Table of Contents were not ready in time'); })]);
+	});
+
+	it('should show error message if config.yml file not found', function(): void {
+		bookTreeViewProvider.getBooks();
+		should(bookTreeViewProvider.errorMessage.toLocaleLowerCase()).equal(('ENOENT: no such file or directory, open \'' + configFile + '\'').toLocaleLowerCase());
+	});
+	it('should show error if toc.yml file format is invalid', async function(): Promise<void> {
+		await fs.writeFile(configFile, 'title: Test Book');
+		bookTreeViewProvider.getBooks();
+		should(bookTreeViewProvider.errorMessage).equal('Error: Test Book has an incorrect toc.yml file');
+	});
+
+	this.afterAll(async function () {
+		if (fs.existsSync(rootFolderPath)) {
+			rimraf.sync(rootFolderPath);
+		}
+	});
+});
+
+
+describe('BookTreeViewProvider.getSections', function (): void {
+	let rootFolderPath: string;
+	let tableOfContentsFile: string;
+	let bookTreeViewProvider: BookTreeViewProvider;
+	let folder: vscode.WorkspaceFolder;
+	let expectedNotebook2: ExpectedBookItem;
+
+	this.beforeAll(async () => {
+		rootFolderPath = path.join(os.tmpdir(), `BookTestData_${uuid.v4()}`);
+		let dataFolderPath = path.join(rootFolderPath, '_data');
+		let contentFolderPath = path.join(rootFolderPath, 'content');
+		let configFile = path.join(rootFolderPath, '_config.yml');
+		tableOfContentsFile = path.join(dataFolderPath, 'toc.yml');
+		let notebook2File = path.join(contentFolderPath, 'notebook2.ipynb');
+		expectedNotebook2 = {
+			title: 'Notebook2',
+			url: '/notebook2',
+			previousUri: undefined,
+			nextUri: undefined
+		};
+		await fs.mkdir(rootFolderPath);
+		await fs.mkdir(dataFolderPath);
+		await fs.mkdir(contentFolderPath);
+		await fs.writeFile(configFile, 'title: Test Book');
+		await fs.writeFile(tableOfContentsFile, '- title: Notebook1\n  url: /notebook1\n- title: Notebook2\n  url: /notebook2');
+		await fs.writeFile(notebook2File, '');
+
+		let mockExtensionContext = TypeMoq.Mock.ofType<vscode.ExtensionContext>();
+		folder = {
+			uri: vscode.Uri.file(rootFolderPath),
+			name: '',
+			index: 0
+		};
+		bookTreeViewProvider = new BookTreeViewProvider([folder], mockExtensionContext.object);
+		let tocRead = new Promise((resolve, reject) => bookTreeViewProvider.onReadAllTOCFiles(() => resolve()));
+		let errorCase = new Promise((resolve, reject) => setTimeout(() => resolve(), 5000));
+		await Promise.race([tocRead, errorCase.then(() => { throw new Error('Table of Contents were not ready in time'); })]);
+	});
+
+	it('should show error if notebook or markdown file is missing', function(): void {
+		let books = bookTreeViewProvider.getBooks();
+		let children = bookTreeViewProvider.getSections([], books[0].sections, rootFolderPath);
+		should(bookTreeViewProvider.errorMessage).equal('Missing file : Notebook1');
+		// Rest of book should be detected correctly even with a missing file
+		equalBookItems(children[0], expectedNotebook2);
+	});
+
+	this.afterAll(async function () {
+		if (fs.existsSync(rootFolderPath)) {
+			rimraf.sync(rootFolderPath);
+		}
+	});
+});