You can learn more about Junit4 at the official documentation website.

Step 1: Run A Local Test

1. Open up your project pane and find the androidTest and test folders.

Okay, time to run your first test.

2. Open the test folder until you find the ExampleUnitTest.kt file.
3. Right-click on it and select Run ExampleUnitTest.

You should see the following output in the Run window at the bottom of the screen:

Step 2: Make the Test Fail

Let's quickly see what a failed test looks like.

1. Copy over the the statement assertEquals(3, 1 + 1):

ExampleUnitTest.kt

class ExampleUnitTest {

   // Each test is annotated with @Test (this is a Junit annotation)
   @Test
   fun addition_isCorrect() {
       assertEquals(4, 2 + 2)
       assertEquals(3, 1 + 1) // This should fail
   }
}

This is checking that 3 is equal to 1 + 1. Because this is not true, this should fail.

2. Run the test.

You should see an x next to the last test:

Quiz

Look at the code and answer the following questions.

1.
2. class ExampleMultiplicationTest {
3.
4.    fun check(){
5.       var result = MathUtil.multiply(2,3)
6.       assertEquals(result, 6)
7.    }
8. }