Martin Rechsteiner Banking on testing How we do testing at DNB 

A bit about our apps • Team of 13 iOS developers in total between Spare, Sbanken and DNB mobile bank. • Monorepo with around ~400 000 lines of Swift. • Mature codebases (mobile bank codebase is around 6 years old, Spare a few more) 

Move fast and not break things • Many critical features that can’t break. • Developers need to be able to con fi dently change code. • It’s important to continuously refactor and improve the codebase. Legacy code is code that you don’t dare to touch. • Automated testing is crucial to maintaining con fi dence in your changes. 

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A brief intro to Parrot • An internal framework for simulating and generating test data. • Roughly speaking, it consists of three parts: • A fake HTTP server • A JSON templating language • Factories 🏭 

What we use Parrot for • Faking APIs when developing new features. • Reproducing edge-cases when doing manual testing. • Generating models and test data in our unit tests. • Ensuring stable, reproducible UI tests. • Demo mode. 

Before Parrot • Each service had a “mock” implementation that returned mock data. • Required a lot of development to simulate the same behaviour as the actual services. • Quickly got out of sync with the actual implementation. • Not really testing our services. protocol AccountsServiceType { func fetchAccounts(completion: ((Result<[Account], E -> } final class AccountsService: AccountsServiceType { ... } final class MockAccountsService: AccountsServiceType { func fetchAccounts(completion: ((Result<[Account], E -> completion?(.success([ Account( ... ), Account( ... ), Account( ... ) ])) } } 

Faking network requests accounts.json invoices.json balances.json DNB • Allows us to fake our APIs on the HTTP level, instead of creating lots of mocks and stubs. • Uses JSON fi les to make it easy to copy the payload from our test environments. • Allows us to control failures, loading times etc. FakeServer 

{ "data": [ { "accountNumber": "1204XXXXXX5", "accountIdentifier": "5", "providerId": "NO_Sbanken", "providerType": "External", "viewType": "EXTERNAL_CARD", "displayBalance": { "value": "200", "currency": "NOK" }, "creditLimit": { "value": "100", "currency": "NOK" }, "bookedBalance": { "value": "100", "currency": "NOK" } } ] } server.on( AccountEndpoint.accounts, response: .template("accounts.json") ) 

Imports { "data": [ import "payment_card.json", import "payment_card.json", import "payment_card.json" { "cardType": "DEBIT", "cardStatus": "NEW_CARD_ORDERED", "lastFourDigits": "0000", "maskedCardNumber": "************0000", "displaySourceProductName": "DNB Kortet", "cardPresentation": "DEFAULT_VISA" } ] } 

Variables { "data": { "accountNumber": {{ accountNumber }}, "type": "Brukskonto", "alias": {{ alias }}, "openingDate": "2010-01-31", "ownerName": "Ola Nordmann" } } return .template( "account_details.json", variables: [ "accountNumber": "10000", "alias": "Brukskonto" ] ) 

Request variables { "data": { "id": {{ uri.id }}, "accountNumber": {{ body.accountNumber }}, "accountName": {{ body.accountName }} } } POST /accounts/:id { "accountNumber": "1000", "accountName": "Brukskonto" } 

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Scenarios • Uses the folder structures to represent scenarios. • Each folder is a scenario, where each fi le is an override for the default scenario. • Sub-folders can be used to create sub-scenarios. • Great when developing features, fi xing bugs or doing manual testing. 

Debug panel 

UI testing 

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UI testing • Parrot makes our UI tests fast and stable. • Simulating speci fi c scenarios in UI tests allows us to cover very speci fi c edge-cases. • By simulating server-side logic, we can make our UI tests more accurate, without the fl akiness of reaching out to our backend systems. 

func testCreateBSU() { let app = XCUIApplication(scenario: AppScenario.testsProductCatalogBsu) app.launch() openProductCatalog(app) XCTContext.runActivity(named: "Go to BSU consent page") { _ in let openDetailButton = app.buttons["BSU"].firstMatch openDetailButton.tap() let title = app.staticTexts["Home savings scheme for young people"].firstMatch XCTAssertTrue(title.waitForExistence(timeout: 1)) let openButton = app.buttons["Next"].firstMatch XCTAssertTrue(openButton.waitForExistence(timeout: 1)) XCTAssertTrue(openButton.isEnabled) openButton.tap() } UI testing specific scenarios 

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Simulating server-side logic server.on(Self.deleteDirectDebit(":id")) { request, requestCache in try requestCache.update("agreement_direct_debits.json") { directDebits in if let directDebitsArray = directDebits.array { directDebits = .array(directDebitsArray.filter { $0.objectId ?. string != request.uri.id }) } } return .empty() } 

Unit testing 

Unit testing services • When unit testing services, we prefer to have the test data inline instead of using JSON fi les. • We can setup speci fi c responses for a given endpoint. • Clearer when the test data is right there in the test. func testMessagesSuccess() async { let endpoint = InboxEndpoint.messages(id: "0") fakeServer.registerRoute(FakeRoute( path: endpoint.path, method: endpoint.method.rawValue, response: .jsonObject([ "data": [ [ "senderName": "DNB Bank ASA", "subject": "Interest rate change", "body": "Interest rate has changed", "created": "1970-01-30T10:32:23+0200", "attachments": [] ], [ "senderName": "DNB Bank ASA", "subject": "Interest rate change", "body": "Interest rate has changed", "created": "1970-01-30T10:32:23+0200", "attachments": [] ] ] ]) )) let messages = await inboxService.fetchMessages(id: "0") 

Factories struct InboxMessageFactory: AttributesFactory { typealias Output = InboxMessage static var defaultAttributes = Attributes([ "senderName": "DNB Bank ASA", "subject": "Interest rate change", "body": "Interest rate has changed", "created": "1970-01-30T10:32:23+0200", "attachments": [ InboxMessageAttachmentFactory.attributes() ] ]) .uuid("id") } 

func testMessagesSuccess() async { let endpoint = InboxEndpoint.messages(id: "0") fakeServer.registerRoute(FakeRoute( path: endpoint.path, method: endpoint.method.rawValue, response: .jsonObject([ "data": [ [ "senderName": "DNB Bank ASA", "subject": "Interest rate change", "body": "Interest rate has changed", "created": "1970-01-30T10:32:23+0200", "attachments": [] ], [ "senderName": "DNB Bank ASA", "subject": "Interest rate change", "body": "Interest rate has changed", "created": "1970-01-30T10:32:23+0200", "attachments": [] ] ] ]) )) let messages = await inboxService.fetchMessages(id: "0") switch messages { case let .success(response): XCTAssertEqual(response.map(\.subject), [ "Message 1", "Message 2" ]) func testMessagesSuccess() async { let endpoint = InboxEndpoint.messages(id: "0") fakeServer.registerRoute(FakeRoute( path: endpoint.path, method: endpoint.method.rawValue, response: .jsonObject([ "data": [ InboxMessageFactory.attributes([ "subject": "Message 1" ]), InboxMessageFactory.attributes([ "subject": "Message 2" ]) ] ]) )) let messages = await inboxService.fetchMessages(id: "0") switch messages { case let .success(response): XCTAssertEqual(response.map(\.subject), [ "Message 1", "Message 2" ]) 

Creating Swift instances func testShowsEmptyStateWhenNoMessages() throws { let viewModel = createViewModel() viewModel.conversationsState = .success([ InboxConversationFactory.build { $0.title = "A" }, InboxConversationFactory.build { $0.title = "B" } ]) let components = viewModel.components() XCTAssertComponent(in: components, be: ListComponent.self) { component in let items = component.items() XCTAssertEqual(items.count, 2) XCTAssertItem(at: 0, in: items, be: InboxConversationListItem.self) { item in XCTAssertEqual(item.conversation.title, "B") } 

Creating Swift instances func testShowsEmptyStateWhenNoMessages() throws { let viewModel = createViewModel() viewModel.conversationsState = .success([ InboxConversationFactory.build(), InboxConversationFactory.build(), InboxConversationFactory.build(), InboxConversationFactory.build(), InboxConversationFactory.build(), InboxConversationFactory.build(), InboxConversationFactory.build(), InboxConversationFactory.build(), InboxConversationFactory.build(), InboxConversationFactory.build(), InboxConversationFactory.build() ]) let components = viewModel.components() XCTAssertComponent(in: components, be: ListComponent.self) { component in let items = component.items() 

Test data in SwiftUI Previews #Preview { InboxMessageView( message: InboxMessageFactory.build { $0.attachments = [ InboxMessageAttachmentFactory.build(), InboxMessageAttachmentFactory.build(), InboxMessageAttachmentFactory.build() ] }, theme: theme, onSelectAttachment: { _ in } ) } 

Benefits of factories • Reduces a lot of boilerplate when writing tests and previews. • By only overriding speci fi c properties, the tests communicate clearly what the actual requirements are for the test to pass. 

protocol Factory { associatedtype Output static var defaultValue: Output { get } } extension Factory { static func build(_ callback: (inout Output) -> Void = { _ in }) -> Output { var value = defaultValue callback(&value) return value } } 

Demo 

Thank you! Martin Rechsteiner @rechsteiner