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Construct high-quality Android UI: Embrace test-driven improvement with Jetpack Compose | by Alejandro Zurcher | July 2023

Protecting this in thoughts, let’s arrange our improvement setting. On this case, we are going to begin a brand new venture with Compose, assuming that this step has been accomplished for the needs of this pattern.

I created a default venture utilizing Android Studio’s templates for Exercise + Compose. Let’s ensure that our venture consists of all the required libraries to implement TDD in Compose:

Lastly, if we select to comply with the Check Pushed Growth (TDD) method, it’s important to bear in mind and comply with the three guidelines of TDD outlined by Robert C. Martin, also referred to as Uncle Bob. These guidelines function our evolving visitors lights🚦when writing or updating any exams within the app:

1. Solely write manufacturing code to move a failed unit take a look at.

2. Do not write extra unit exams than sufficient to fail (compiler failure is failure).

3. Do not write extra manufacturing code than essential to move a failed unit take a look at.

By following these guidelines, we be sure that our improvement stays centered and environment friendly.


The Design Spec is prepared and the setting is ready up, so How will we method a brand new UI piece with a take a look at?

This may rely on every framework used for the UI, on this instance we are going to use Jetpack Compose to know the way toIdeas in Drafting“

With Compose, you possibly can simply divide the person interface into very small items described as Composes that will likely be stitched collectively to render the complete UI.

So the very first thing we have to do is take an in depth have a look at the UI to find out how we are able to break up it and go from small to giant.

At a look, I’ve recognized (no less than) 5 totally different Artificial Gadgets that can match this show:

  • The highest motion bar consists of Again, Title, Merchandise Rely, and Filter actions.
  • Foremost record of clothes objects
  • Each merchandise of clothes
  • Clothes merchandise content material (show title, value, and add to cart motion button)
  • Favourite button

There was some added worth in doing this as we are actually beginning to present each reusable parts reminiscent of the highest motion bar and in addition beginning to consider naming our composable merchandise with out even touching a single line of code.

So let’s go forward and choose the smallest composable one from our new display; Favourite button.

Assuming this button acts like several favourite button, it must assist 2 states; full coronary heart and empty coronary heart. Let’s write our first take a look at:

It’s price mentioning at this stage that we are going to comply with the proposed materials on Check Compose so we additionally want extra compose TestRule and initialize our display utilizing it setContent perform:

Now let’s put in our take a look at situation

🔴 And once we wrote our Combinable title (the title would not exist but), we broke the second TDD rule; the take a look at now not compiles


To unravel this, we create a brand new Kotlin file and write our Composable

This may make now

And we’re again to the take a look at

Inexperienced means good

🟢 Compilation drawback solved! We are able to proceed writing exams now

So the take a look at is prepared and compiled, subsequent step; let’s run it

🔴 We did it; we’ve got a failed take a look at now. Please comply with TDD rule 1 and a couple of to move earlier than writing any new exams.

And I do know what you are considering, we do not test for boolean! We do not assist different eventualities, we are able to write much more code! However right here, that is the precise level the place you must choose that hat and select the TDD hat If you wish to do the conversion and just one assume: Will we comply with all of the TDD guidelines? Nicely, that is okay, let’s transfer on.


🟢 The take a look at is now fully inexperienced, which implies we are able to write the subsequent take a look at. So let’s strive one other situation our compositing must assist, present a empty coronary heart if isFavorite To be WRONG.

🔴 And once we run it:

So once more, following TDD rule #1 & 3, we return to our aggregation and add the logic wanted to move this take a look at, being cautious sufficient that our earlier take a look at additionally works.

And we ensure that to run the entire set now in order that each exams are run:

🟢 And now we are able to see all of our exams go inexperienced!

Lastly, we are able to replace our exams to make sure that the opposite icon would not present up within the incorrect scenario.

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Updated: July 25, 2023 — 9:08 am

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