How to tdd your mvp

How to TDD your MVP
Testing Android (mobile) apps
Michał Bujalski
Android Developer at TSH

Plan
- Why to test your apps
- Model-View-Presenter
- Unit Testing Android apps
- Test-Driven-Development
- Demo

Why u not test your code?
- testing takes a lot of time

- ASAP-Driven-Development

- our code is not testable so we don’t write tests
- we don’t write tests because our code is not testable

Why you should test your apps?
- give you confidence
- tests save time
- make easier to add new features
- make easier refactor
- testable, clean code

Testing mobile apps - problems
- big blocks of code
- deeply coupled with OS components
- MVC - View layer blends into Controller

MVP vs MVC
- MVC not always suitable for systems heavily tied with UI
- View and Controller often blend with each other

Model-View-Presenter
View
- contains no logic
- contains all view references
- controls the state of platform components (TextView, ImageView)

Presenter

Presenter
- contains ALL the logic necessary to present model on the view
- contains NO Framework or SDK references (Context, ContentProviders)

Model
- contains logic necessary for obtaining data ( API fetch, cache handling, db
calls)

data class Contact(val name:String)
interface ContactsContract{
interface View{
fun setData(contacts:List<Contact>)
}
interface Presenter{
fun fetchContacts()
}
}

class ContractsActivity: AppCompatActivity(), ContactsContract.View{
lateinit var presenter: ContactsPresenter
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
presenter = ContactsPresenter(this)
}
override fun setData(contacts: List<Contact>) {
//set data to adapter
}

class ContactsPresenter(
private val view: ContactsContract.View
private val repository: ContactsRepository
): ContactsContract.Presenter {
override fun fetchContacts() {
//called contacts fetched
view.setData(emptyList())
}
}

- UI logic is written purely in Java/Kotlin
- testable
- does a lot of heavy lifting for Activities/Fragments/ViewControllers

Unit Testing in Android
- Junit
- Mockito
- Robolectric

Unit Testing in Android - Mockito
whenever(repository.fetchContacts()).thenReturn(emptyList())
verify(view).setData(any())
verify(view, never()).setData(any())
verify(view, times(2)).setData(any())
...
val inOrder = inOrder(view,repository)
inOrder.verify(view).showProgress()
inOrder.verify(view).hideProgress()

Unit Testing in Android - Robolectric

You don’t need Robolectric

Robolectric
- adds more unnecessary dependencies (e. g. API version)
- encourages coupling your logic (and tests) with Android SDK
- hard to maintain

Unit Testing in Android
If you need SDK components in your unit tests
- you are doing something wrong
Andrzej Sz.

Test-Driven-Development
Write tests before you start implementing feature

1. Write your tests
2. Make your code compile
3. Run your tests
4. If tests fail, fix implementation and goto 2 else goto step 4.
5. Refactor
6. Stop

- tests are part of development process
- concentrate on what the code should look not on how should it be
implemented
- test are actually code documentation
- test coverage for free

Test-Driven-Development - writing test scenarios
Contacts list

Contacts list
- fetch contacts from API
- show result on view
- if any error is returned present error on view

Contacts list
Given
api returns valid data
When
List update is called
Then
View should receive update

@Mock lateinit var view:ContactsContract.View
@Mock lateinit var repository: ContactsRepository
lateinit var presenter:ContactsContract.Presenter
@Test
fun `fetch contacts, success`(){
//given
whenever(repository.fetchContacts()).thenReturn(emptyList())
//when
presenter.fetchContacts()
//then
verify(view).setData(any())
}

Contacts list
Given
api returns no connection error
When
List update is called
Then
Show network error

@Mock lateinit var view:ContactsContract.View
@Mock lateinit var repository: ContactsRepository
lateinit var presenter:ContactsContract.Presenter
@Test
fun `fetch contacts, network error`(){
//given
whenever(repository.fetchContacts()).thenThrow(NetworkError())
//when
presenter.fetchContacts()
//then
verify(view).showNetworkError()
}

- simple
- test one story at time
- test small part of functionality

Test-Driven-Development - Demo
- Kotlin
- RxJava
- Mockito
- Mockito-Kotlin
- RxKotlin
- RxAndroid

Test-Driven-Development - Demo
- https://github.com/michalbujalski/TDDExample

TDD your MVP
- unit testing is every developer’s responsibility
- tests SAVE time
- don’t mock what you don’t own, don’t test the framework
- make writing tests part of your development process NOT the result

How to tdd your mvp

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