Mobius

Mobius is our recommended architecture for building Android applications. We also feel that it is much easier to learn Test-Driven Development by starting out to build apps using Mobius.

Day 1: Introduction to Mobius & TDD (4:50 hours)

• Theory: Introduction to Mobius (1 hour)

  • Eliminating the moving parts using functional programming

  • Pure functions

  • State transition diagrams

  • Model & Event

• Pairing Activity: The counter app state transition diagram (1 hour)

  • The update() function

  • Introducing the UpdateSpec class

  • Test driving the counter update() function

  • Wiring the update() function to the UI

• Theory: Test-Driven Development (30 minutes)

  • Principles of TDD

  • ​YAGNI

  • The red, green, and refactor cycle

  • TDD as a design practice

• Recap (20 minutes)

  • Key takeaways

  • Reading materials for the next day

    • ​https://github.com/spotify/mobius/wiki/Concepts​

    • ​https://blog.cleancoder.com/uncle-bob/2016/03/19/GivingUpOnTDD.html

Day 2: Mobius Effects & Effect Handlers (5:05 hours)

• Reflection of Day 1 and discussion around reading materials (30 minutes)

• Pairing Activity: Login Screen update() Exercise (2 hours)

  • Introducing effects & effect handlers

  • Login example state transition diagram

  • Test driving the login update() function

  • Identifying the primitive obsession code smell (Watch this)

  • The “What to test?” problem

  • Relationship between the number of execution paths and tests

  • Test driving the Username and Password classes

  • Modeling async state transitions

  • Completing the update() function

• Pairing Activity: Materializing effects using effect handlers (1:30 hours)

  • State verification vs. behavior verification

  • Introduction to Mockito

  • Low confidence behavior verification tests

  • Writing the first effect handler

  • Using the RxJava SubtypeEffectHandler

  • Action, Consumer, and ObservableTransformer

  • Errors of first-class citizens

  • Using Scheduler in tests

• Pairing Activity: Introduction to Views and View Renderers (45 minutes)

  • Using mockito to verify view rendering logic

• Recap (20 minutes)

  • Key takeaways

Day 3: Mobius, the final bits (5:35 hours)

• Reflection of Day 2 (30 minutes)

• Pairing Activity: Creating the shell (45 minutes)

  • Wiring all the Mobius components

  • Saving and restoring model state

  • The @Parcelize annotation

  • Caveats of saving data using Android’s Parcelable interface

• Pairing Activity: Subtle bugs introduced by async operations (45 minutes)

  • Handling normal flow of execution using the init() function

  • Handling edge cases using the init() function

  • Using the InitSpec for testing normal flow and edge cases

• Recap (20 minutes)

Day 4, 5, and (possibly 6): Building the NASA APOD Apps (14:50 - 22:50 hours)

• Reflection of Day 3 (20 minutes)

• Individual Activity: NASA APOD Application (8 - 16 hours)

  • Step 1: Drawing the state transition diagram

  • Step 2: Writing the init()the update() tests

  • Step 3: Writing Effect Handler tests

  • Step 4: View and View Renderer Tests

  • Step 5: Wire up the imperative shell

• Code review and addressal (1:30 hours)

• Recap (1 hour)

Points of Confusion

• Effect are more closer to intention for side-effect than performing a side-effect

• Representing decision making in state diagram