Learn what is mockito and why to implement Unit Testing using Mockito in Android in this tutorial. You can also visit the Github Source for code implementation

1. Unit Testing
Using
Mockito in
Android
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2. Introduction

3. Nowadays mobile applications are getting
complex functionalities & bigger in size, that’s
why writing test cases is very important to
refine code and make sure that each module
works properly (I know it is often
underestimated among the mobile developer
community, sometimes totally ignored!). To
write code that is efficiently unit-testable, we
should use the best suitable architecture like
MVP or MVVM which carries loose coupling
into the Android activities/fragments/adapter.

4. Three different tests developers should
consider adding in their test suits:
1. UI Tests: These tests are for asserting
application UI. Espresso is used.
2. Instrumented Tests: When we want to verify
user actions like button click etc these tests run
on Android devices, whether physical or
emulated taking the advantage of APIs provided
by the Android framework. AndroidX Test &
Espresso is widely used for the same.
3. Unit Tests: Unit tests are more important for
testing every function and procedure in the
application. For unit testing, mostly used tools
are JUnit, Mockito, or Hamcrest.
The main objective of Unit Testing is to fix bugs
early in the development cycle by verifying the
correctness of code. In this tutorial, we will
learn how what is Mockito and the steps to
implement unit testing using Mockito in
Android application.

5. Why Mockito?

6. Often we have classes with dependencies and
methods being dependent on another method
of a different class. When we are unit testing
such methods, we want the unit tests to be
independent of all other dependencies. That’s
why we will Mock the dependency class using
Mockito and test the main class. We can not
achieve this using JUnit.

7. Hire Android developer from
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generations of developers at
Bacancy.

8. Steps: Unit
Testing Using
Mockito in
Android

9. Let’s take a simple example of computations
like addition, subtraction, etc to understand the
Mockito framework.
We will create a file ComputationActivity.kt to
display all computations upfront. For managing
all operations we will create object class
Operations.kt which will be passed to
ComputationActivity class as a param in the
primary constructor.
class ComputationActivity(private val
operators: Operations) {
fun getAddition(x: Int, y: Int): Int =
operators.add(x, y)
fun getSubtraction(x: Int, y: Int): Int =
operators.subtract(x, y)
fun getMultiplication(x: Int, y: Int): Int =
operators.multiply(x, y)
fun getDivision(x: Int, y: Int): Int =
operators.divide(x, y)
}

10. Operations.kt class will look like this which will
handle computation functions.
object Operations {
fun add(x: Int, y: Int): Int = x + y
fun subtract(x: Int, y: Int): Int = x - y
fun multiply(x: Int, y: Int): Int = x * y
fun divide(x: Int, y: Int): Int = x / y
}
Add dependencies needed to integrate Mockito
in the build.gradle file.
We will use testImplementation which applies
to the local test source, not the application.

11. testImplementation 'junit:junit:4.13.2'
testImplementation
'org.mockito:mockito-core:2.25.0'
testImplementation
'org.mockito:mockito-inline:2.13.0'
Folder structure for adding ComputationTest.kt
file for testing ComputationActivity.kt class.
By default, module-name/src/test will be
having source files for local unit tests.

12. @RunWith – we have annotated with
MockitoJUnitRunner::class which means it
provides the Runner to run the test.
@Mock– Using @Mock annotation we can
mock any class. Mocking any class is
nothing but to create a mock object of a
particular class.
Now, we will add test functions in our
ComputationTest.kt file
Here we will mock the Operations.kt class in
our test file as ComputationActivity.kt file has a
dependency on it.

13. @RunWith(MockitoJUnitRunner::class)
class ComputationTest {
@Mock
lateinit var operators: Operations
lateinit var computationActivity:
ComputationActivity
}
@Before– Methods annotated with the
@Before annotation are run before each
test. In case you want to run common code
this annotation is very useful. Here we are
initializing ComputationActivity class in
our testing file before running Tests with
the help of @Before annotation.

14. @Before
fun setUp(){
computationActivity =
ComputationActivity(operators)
}
@Test– To perform the test we need to
annotate the function with @Test.
@Test
fun
givenValidInput_getAddition_shouldCallAddO
perator() {
val x = 5
val y = 10
computationActivity.getAddition(x, y)
verify(operators).add(x, y)

15. The verify method will check whether ta
particular method of a mock object has been
called or not.
@After– @After annotation is used to run
after each test case completes.
@BeforeClass– @BeforeClass is used when
you want to run a common operation that’s
too expensive to run multiple times. So,
with this annotation, you can execute such
an operation before running all other test.
@AfterClass– Used for deallocation of any
reference after all tests executed
successfully.

16. Mock marker inline: Mockito can’t test final or
static classes directly. As we know, Kotlin
classes are by default final. So to run tests for
these classes, we need to add marker inline
dependency.
Mockito 2.25.0 had released an important
feature for developers who uses mockito-inline.
To be specific, anyone using Kotlin, which
demands using mockito-inline. Moving towards
our last section of Unit Testing using Mockito in
Android tutorial and run the tests.

17. Run the Tests

18. To execute all tests, right-click on
ComputationTest.kt file & select the option
Run
You can even run only one test function by
right-clicking on that function & selecting the
Run option from there.

19. Github Source:
Unit Testing in
Android

20. Feel free to visit the source code: mockito-
android-testing and play around with the code!

21. Conclusion

22. Mockito is used to test final classes in
Kotlin.
Mockito is a widely used framework for
mobile developers to write unit tests.
So, this was about unit testing using Mockito in
Android application. We have more tutorials
related to mobile development for you! If you
are someone who is looking for Android or iOS
tutorials to start with, then the Mobile
Development tutorials page is for you! Vist the
tutorials and start learning more! You can write
us back if you have any questions or
suggestions! We are happy to help!

23. Thank you
https://www.bacancytechnology.com/