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Test driven software design of an Android application

Concerning validation of an Android application, are there any points for writing lines of codes to be simply testable (both manual and automatic tests) ?

In my opinion, testing small applications is not a top priority (since they suppose to be implemented fast and quickly and most of the time they serve a small purpose) and you can be skeptical with that since not writing test can save a bit of time. therefore no need to write the code in a way that is testable too.
But remember a few things:
Writing a testable code is a skill that an intermediate developer must have.
A testable code will lead to a maintainable code and that is very important for applications that have a future (almost all of them)
adding features is a lot easier when you have tests on.
Building a team and even passing the code to another person to maintain/add new features is a lot easier with a testable app.
As far as I know, in android testable code means architected code and architecture is compulsory for almost all applications.
Testable codes need to be following coding standards like SOLID Principles
Maintain code in layers, such as separate classes for Api calls and make separate classes for views that you are using at multiple places in Application
Don't write too much code in activities, and don't make functions too long that you have to deep search for piece of code after some time.
Try to write comments frequently, so that some one can understand your code easily
thus try to learn how to write testable and do your best to write test. It will pay off before you know it
Update
to run your test automatically you can use a CI server.
there are lots of option on how to create and configure one. but there are plug and play options as well.
but for further details you can read official Android Developer Doc
hope I answered your question

The following link dirrects us to Test Driven Development:
https://developer.android.com/training/testing/fundamentals

What are the pros and cons of android data-binding?

Both of my colleague and I have experience in MVVM of Web App, while we are new to native android development. Now we have contrary opinions about android data-binding -- I'm a fan of it while he is not.
My Arguments:
Reduces boilerplate code which in turns brings
Less coupling
Stronger readability
Powerful, easy to implement custom attribute and custom view
Even faster than findViewById (details)
His Arguments:
The auto-generated .class increases app size.
Harder to debug
I've made some investigation but there are not many discussions about it. Now I want to collect the pros and cons of android data-binding.
Aspects of discussion include but are not limited to:
unit test
app size
performance
learning curve
readability
coupling

I will comment on your arguments first then I will state my opinion:
1.Remove boilerplate code - it will remove some it will just move some in the xml or it will require additional classes. So you have to be careful and balance the use of data binding.
2.Stronger readability - depends if you are a new developer then you may find it easy to learn it but if you previously worked on android you will need extra time to learn it.
3.Powerful - the code has more power, you can implement whatever you like in code. Think about it like this, everything you implement using data binding has a code equivalent (it might be longer and more code to write), but the revers is not valid.
4.Even faster than findViewById - comparing the speed between these two, in my opinion is useless, you will never notice the difference, if you see some difference, then one of the implementation is wrong.
5.Auto generated class - it's true it will increase the app size, but again only if you have tons of it it will matter. It's true that on the android dev web site they state that it's kind of bad to use libraries that create autogenerated code or annotations that will generate extra code.
6.Hard to debug - depends, like readability, of what you are used to, heck debugging is hard either way for some problems, and you will get better by debugging not by using a different library.
So this is pure my opinion, I've developed many apps using different libraries and different approaches, and they all had pros and cons, but what I've learn: balance everything, don't use tons of libraries, don't waste time implementing things that are implemented already and work well, don't "decouple everything", don't "couple" everything, don't use code only, don't try to "generate" everything.
I think it's quite wrong, and you can get a wrong idea, if you ask for 'pros & cons' about some library/implementation, because usually it won't be impartial, you will get a lot of pros from somebody who used the library in a specific way and it worked and others will give you cons because they used different and it didn't work.
So in conclusion, I think you should check what the library can do for you and what can't do for you and decide if it's good for your setup. In other words, you should decide if a library is good for you not other people ;).
Update - 8 August 2018
First of all I still stand with my initial conclusion, balance is the key in these kind of situations, but in my case, data-binding speed-up a little bit the development process and also improved it. Here are a few new points that you should all think about.
Testing the UI -- with data-binding it's much more easy to test the UI, but data-binding it's not enough for that, you also need a good architecture and using the Google suggested architecture will show the actual power of data-binding.
The most visible changes were provided for points 2 & 5 from my original answer. It kind of was easier to read the code after we decided to use data-binding, and the most important thing here is: we as a team decided that we will use data-binding and after that, we kind of expected to have most of the trivial and basic UI setup in the XML file.
For the debugging part, here's a little bit tricky, Android Studio has a lot to improve on the errors and autocomplete for the data-binding but the most common errors you'll get them after the first 2-3 occurrences. Also I've learned that a "clean project" form time to time, helps A LOT.
Another point that you'll have to take in consideration is the project configuration to use data-binding, right now AS (3.1) supports by default data-binding (just set a flag in graddle) for Java, but I had some issues with Kotlin, after a bit of search here on SO, I managed to fix everything.
As a second conclusion (from my original post), if you can and the project deadline/requirements/etc allows you to try data-binding, go for it it will worth (unless you do some really stupid stuff :)) ).

I am working on a huge Android project and the team has decided to phase out Data Binding library. Why? The primary reason is that it is exacerbating build time(10+ mins), by generating a lot of classes in the build process.

Even if i like danypata's answer i would like to add/edit some of his statements to android databinding.
1.Remove boilerplate code - As written in danypatas answer it removes some code and adds some code somewhere else like in layouts. That doesnt mean that the boilercode isnt reduced because usually it is reduced.
For example you may want to create a bindingadapter, which handles several custom arrayadapters for your spinner/recyclerview/listview/.. but requires only one simple adapter. You may want to use the adapter in your layout by using e.g.
app:myCoolAdaptersData="#{model.mydata}"
Now you can create your generic adapter and (re)use your bindingadapter in all your layouts instead of using for example:
ListView lv = findViewById(...);
CoolGenericAdapter<MyModel> coolAdapter = new CoolGenericAdapter<>(...);
lv.setAdapter(coolAdapter);
This is just one simple example which recudes the code alot in larger projects. Another sample to recude code is, that you bind your model to your layout. Updating field-values of your model usually updates your model aswell (if its at least a BaseObservable/ObservableField).
That means that you dont need to find all your views, update your views, update your models, ...
2.Stronger readability - The extra time spent for learning databinding doesnt really matter. Since the layouts are not really different except that you wrap them into a layout tag and put your namespaces there, it doesnt really differs from "regular" layouts. Using bindingadapters and accessing the model in the layout may take some time, but usually you can start beginning with the basics which are easy and beautiful to use aswell. Learning new stuff always takes time, but you will easy overhaul the time when using databinding after a while.
3.Powerful - Yes, its very powerful. Its easier to reuse existing code, reuse existing bindingadapters and may lead to more generated code but thats not always true. For example you may create multiple adapters within several classes instead of creating one bindingadapter, it may be hard to "optimize" it later. Optimizing the Bindingadapter means that it gets updated everywhere. Optimizing may decrease the "lines of code" since the boilerplace is reduced anyway.
I agree to 4. and 5.
6. Hard to Debug Since AS 3.0+ outputs useful hints like syntax issues in your layout (line number and file) its easy to debug databinding generated code. If you have problems finding the issue you may also want to check for errors in the generated code. Some librarys like dagger 2 or android architecture library may confuse you because the error lines doesnt match with the real "error". This is due generated code by other annotation processors. If you know that those annotation processors may get in trouble with databindings error outputs, you can easy fix that.
7. Unit Testing Its possible like if you dont use databinding by using executePendingBindings.
8. Readability Readability may be better without databinding. Since you put some business logic into your layout, some into your real code, it may lead to spaghetti-code. Another problem is that using lambdas in your layout may be very confused if the "layout-designer" doesnt know which param may be used.
Another very big problem is that bindingadapter can be everywhere. Using BindingAdapter annotation generates the code. That means that using this in your layout may lead to problems to find the proper code. If you want to update a bindingadapter you need to "find" it.
When should you use what? For larger projects it is a really good idea to use databinding together with the mvvm or mvp pattern. This is a really clean solution and very easy to extend. If you just want to create a small simple application you'r fine using MVC Pattern without databinding. If you have existing generic bindingadapters which can be used from other projects you may want to use databinding, because its easy to reuse this code.

Data binding, concept wise looks promising to me, but I do not like the implementation part.
I would appreciate a bit more simpler and direct approach to it.
Thus I feel lot more comfortable in keeping it old school.
Model classes, mutable objects, observers feel like too much to me, if some how the data variables used for binding are received as Objects that are mutable and observable directly in a class , then that would make the process lot more cleaner, simpler and concise.

Espresso Best Code Architecture

I want to run an Espresso instrumentation test for my application. Test contains navigation to multiple activities and interactions with several widgets.
What could be the best possible coding style I should follow to keep code clear and maintainable.
For now I had create different class for each activity and access static test method as follow:
#Test
public void validateUserNavigationScenario() {
// Create a bitmap we can use for our simulated camera image
SignOnActivity.validateLogin();
ProductSelector.selectProduct();
ProductDetail.showProductDetails();
ProductDetail.addProductToCart();
pressBack();
ProductSelector.selectProduct();
// ... additional test steps and validation ...
}

Coding test code is not different from coding production code.
The same good patterns and habits used for production code should be present in testing code. Using static reference as the main approach to structure all your suits seems to me a bad decision.
You should check it out Jake Wharton's talk about how to structure your testing code.
Instrumentation Testing Robots
It is focus on Kotlin development, but the same principles apply for Java. To sump up, it claims that you should hide your internal details inside some sort of “robot” pattern. Which means that you should try to be as much semantic as possible with your exposing API in order to create readable and maintainable tests.
Think on your test as if they were be used for other devs, and then think that you are one of them. How do you want it to use them?

Trying to fit a "clean architecture" on an iOS app

Recently I’ve been rethinking my android architecture project, trying to adapt it to a more “clean architecture”, specifically, the kind of design suggested by “Uncle Bob”.
Which it involves several layers of abstractions, a nice isolation of responsibilities and a very strong dependency inversion achieved by dependency injection; which, ultimately, leads to a very decoupled-portable system. A perfect candidate to be tested by unit testing and integration testing.
In my android implementation I’ve ended up having three different modules or layers:
-domain: entities, interactors, presenters (pure java module)
-data: (acts as a repository to supply the data to the domain) (android library module)
-presentation: ui related stuff, fragments, activities, views, etc (android application module)
So, I’m trying to figure out what would be the best approach on the iOS ecosystem.
I’ve tried creating a project with multiple targets to achieve the same solution:
-domain: command line target (which seems very weird but I think is the most pure swift target available)
-data: cocoa touch framework
-presentation: cocoa touch framework
With this approach I can use these targets in the way I did with android modules. But the first caveat I’ve found it is that I need to add manually every new file to the dependent target.
But my knowledge is very limited in projects with multiple targets. I mean I’ve never created an iOS application with multiple targets. So I don’t know even if the solution would be use a framework (cocoa touch/cocoa) as a target instead of a command line module for the domain layer.
Any thought would be really appreciate.
Thanks!

Uncle Bob's Clean Architecture absolutely applies to iOS, Swift, and Obj-C. Architecture is language agnostic. Uncle Bob himself codes mostly in Java but in his talks he rarely mentions Java. All his slides do not even show any code. It is an architecture meant to be applied to any project.
Why am I so sure? Because I've studied MVC, MVVM, ReactiveCocoa, and Clean Architecture for 2 years. I like Clean Architecture the best, by far. I tested it by converting 7 Apple sample projects to using the Clean Architecture. I've used this approach exclusively for over a year. It works out better every time.
Some of the benefits are:
Find and fix bugs faster and easier.
Extract business logic from view controllers into interactors.
Extract presentation logic from view controllers into presenters.
Change existing behaviors with confidence with fast and maintainable unit tests.
Write shorter methods with single responsibility.
Decouple class dependencies with clear established boundaries.
We also added a router component so we can use multiple storyboards. No more conflicts.
Writing unit tests is greatly simplified too because I only need to test the methods at the boundaries. I don't need to test private methods. On top of that, I didn't even need any mocking framework because writing your own mocks and stubs becomes trivial.
I've written my experience for my last 2 years studying iOS architecture at Clean Swift I also put together some Xcode templates to generate all the Clean Architecture components to save a ton of time.
UPDATE - To answer #Víctor Albertos's question about dependency injection in the comment below.
This is a really great question and demands a long detailed answer.
Always keep the VIP cycle in mind. In this case, the doSomethingOnLoad() method is not a boundary method. Rather, it is an internal method invoked only within CreateOrderViewController. In unit testing, we test a unit's expected behavior. We give inputs, observe outputs, then compare the outputs with our expectations.
Yes, I could have made doSomethingOnLoad() a private method. But I chose not to. One of the goals of Swift is to make it easy for developers to write code. All the boundary methods are already listed in the input and output protocols. There is really no need to litter the class with extraneous private modifiers.
Now, we do need to test this behavior of "The CreateOrderViewController should do something on load with this request data" somehow, right? How do we test this if we can't invoke doSomethingOnLoad() because it is a private method? You call viewDidLoad(). The viewDidLoad() method is a boundary method. Which boundary? The boundary between the user and view controller! The user did something to the device to make it load another screen. So how do we invoke viewDidLoad() then? You do it like this:
let bundle = NSBundle(forClass: self.dynamicType)
let storyboard = UIStoryboard(name: "Main", bundle: bundle)
let createOrderViewController = storyboard.instantiateViewControllerWithIdentifier("CreateOrderViewController") as! CreateOrderViewController
let view = createOrderViewController.view
Simply calling the createOrderViewController.view property will cause viewDidLoad() to be invoked. I learned this trick a long time ago from someone. But Natasha The Robot also recently mentioned it too.
When we decide what to test, it is very important to only test the boundary methods. If we test every method of a class, the tests become extremely fragile. Every change we make to the code will break many, many tests. A lot of people give up because of this.
Or, think about it this way. When you ask how to mock CreateOrderRequest, first ask if doSomethingOnLoad() is a boundary method that you should write test for. If not, what is? The boundary method is actually viewDidLoad() in this case. The input is "when this view loads." The output is "call this method with this request object."
This is another benefit of using Clean Swift. All your boundary methods are listed at the top of the file under explicitly named protocols CreateOrderViewControllerInput and CreateOrderViewControllerOutput. You don't need to look elsewhere!
Think about what happens if you were to test doSomethingOnLoad(). You mock the request object, then assert that it equals to your expected request object. You are mocking something and comparing it. It's like assert(1, 1) instead of var a=1; assert(a, 1). What's the point? Too many tests. Too fragile.
Now, there is a time when you do mock CreateOrderRequest. After you've verified the correct CreateOrderRequest can be generated by the view controller component. When you test CreateOrderInteractor's doSomething() boundary method, you then mock CreateOrderRequest using interface dependency injection.
In short, unit testing is not about testing every unit of a class. It is about testing the class as a unit.
It is a mindset shift.
Hope that helps!
I have 3 series of draft posts in Wordpress on different topics:
In-depth look at each of the Clean Swift components
How to break up complex business logic into workers and service objects.
Writing tests in Clean Swift iOS architecture
Which one of these do you want to hear more first? Should I bump up the series on testing?

In my opinion Clean Architecture is a set of ideas, rules, principles... to make a code better.
[Android Clean Architecture]
With this approach I can use these targets in the way I did with android modules.
You are able create a target[About](application target or framework target...) but it depends on your needs
If you read Architecting Android...Reloaded from Fernando Cejas
you might have seen that I used android modules for representing each layer involved in the architecture.
A recurring question in discussions was: Why? The answer is simple… Wrong technical decision
The idea is that is not necessary to use some build components to implement Clean Architecture

what to unit test, in android apps

My apps are mostly GUIs that communicate to a server for most of their information. If anything goes wrong it will usually be in the network call or making a wrong assumption about a JSON object.
Unit Tests are not good for these network-related and i/o related tasks, otherwise, they won't be called unit tests.
SO I am trying to gather the point of Unit Tests in my case. Why would I test if an Android button can click or an EditText can see what I type? I just don't understand the utility of implementing these tedious tests
private void initElements(){
placeButton = (Button) findViewById(R.id.currplace);
placeButton.setText(MainActivity.this.getString(R.string.findingLocation));
placeButton.setEnabled(false);
selectplaceLayout = (LinearLayout)findViewById(R.id.selectplaceLayout);
selectplaceLayout.setVisibility(View.GONE);
splash = (RelativeLayout)findViewById(R.id.splashbg);
infoLayout = (LinearLayout)findViewById(R.id.infoLayout);
}
if this above method passed, which all my activities run in onCreate, then I know the app works. A unit test of this would be a redundant time-consuming thing to create. Time-consuming because I am not familiar with all the methods in the jUnit and Android testing framework.
So, long story short, what's the point? Is there a particular way I should be thinking about these tests? All examples and tutorials I've seen so far only talk about the simplest examples, for the sake of brevity, but I cannot think of any practical uses for unit tests in a predominately client-server app.
What am I expected to discover by accessing the android views that I already know I declared and initialized? I must be thinking about this in a too limited way
so, insight appreciated

There are lots of facets in your question, but to my opinion - you probably don't need unit-tests in your project.
Unit tests really shine when you need lots of business logic to your project. In this case you probably want to divide your application into multiple layers (say, 3-tier architecture) to, among other, add some natural isolation for business-logic layer and cover it with safety net of unit tests.
This safety net covers your ass during refactor of the business layer, and that's one of the main things you what from unit tests (TDD can offer some nice extra side effects though).
However, it's not all unicorns and rainbows and unit-test may cost, and sometimes they cost a lot. Good unit tests are isolated (i.e. deal with small chunks of code). This means that you have to add layers of abstraction in order to put your classes under the test.
This may have positive affect on your system or negative one. Layering makes your system more flexible with cost of increased complexity.
Having that said - the value of the unit-tests is proportional to the amount of abstract business-logic you are going to introduce in your project. You may think of it also this way - if it is overkill to add abstract layers to your architecture - don't add unit-tests - they will only make things more complicated (architecture and build wise).
Based on your description - your typical app tend to be pretty much presentation layer for some external server-side. It does not that much except presenting information on android handset and transforms user actions to commands to server-side where main business logic gets done (controlling).
With this approach most of the code you probably write is related to "how to display this and that" or "how to signal server in this and that case". This sort of code is obviously heavily depend on platform and this mean that if you do want to put it under test you'll have to mock lots and lots of Android specific code\behavior.
Now, Android is somewhat specific platform. It was designed to be both performance optimized and allow developers to start and produce apps quickly. Often this means some amount of "swiss-knife" classes you have use\extend and generally this speeds up writing code, but mocking those classes can become a real hell. Not to mention that you have to have understanding of how platform works under the hood to make those mock useful. In other words overhead from making those test is going to be high.
Another thing that is wrong with testing presentation layers is that they tend to change much more dynamically than business layers. And, of course this mean that you'll have to refactor thee tests which adds even more overhead.
I have to say one thing about various utility/helper classes though. Even if these classes are belong to presentation layer and do depend Android code, but do some rather non-trivial logic and it is easy to mock and write unit tests for them, it might actually be a good idea to do this. However, if you do have lots of such code - this is might be a signal that you haven't designed your architecture/layering well, and need to rethink what you are doing.
In the end to answer your question you have to answer these questions first:
Will it be overdesign to add abstract layer that is separated from the platform to your application (seems like in your case it will)? If yes - do not use unit-tests - they will only slow you down. If no - do use them.
Are you going to refactor a lot? If that's large project with lots of code and thus maintenance - you probably will, so invest in layering and unit-tests (but, at a glance, it does not seem that this is your case). If that is not your case - do not bother with unit-tests and go fast.
Do you need to mock platform a lot to write your unit tests? If yes (seems to be your case) - don't write unit tests - they do not worth the effort.
Hope this will help.

UTesting in Android generally takes relevance when you are using some layering with a good architecture. Nowadays the most popular is Clean Arch, which is all about maintainability and testability. Every part of the architecture has exactly one purpose. We just need to specify it and check that it actually does its job every time.
When testing use cases we should test that use case calls correct methods in repositories or executes other use cases. We should also test that use case returns proper callback.
When testing repositories, you should arrange DAOs – make them return or receive some dummy data, and check that repository is handling the data in a proper way.
When testing mappers (converters), specify input to the mapper, and exact output you expect from the mapper, then assert they are equal. Do the same for services, parsers etc.
Leaving the architecture besides any good modular and decoupled design will contain business logic in functions and classes, and if those follow single responsibility principle (they should), then likely should be tested.
Think about testing before and during coding. That way you can write testable and decoupled code. Use your tests as class specification, and if possible write them before the code.
Examples and expanded info: https://five.agency/android-architecture-part-5-test-clean-architecture/

from Android.Docs
For testing Android apps, you typically create these types of automated unit tests:
Local tests: Unit tests that run on your local machine only. These tests are compiled to run locally on the Java Virtual Machine (JVM) to minimize execution time. Use this approach to run unit tests that have no dependencies on the Android framework or have dependencies that can be filled by using mock objects.
Instrumented tests: Unit tests that run on an Android device or emulator. These tests have access to instrumentation information, such as the Context for the app under test. Use this approach to run unit tests that have Android dependencies which cannot be easily filled by using mock objects.
Note: Unit tests are not suitable for testing complex UI interaction events. Instead, you should use the UI testing frameworks, as described in Automating UI Tests.