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

More Related Content

What's hot

Similar to How to tdd your mvp

More from The Software House

Recently uploaded

How to tdd your mvp