Kotlin Programming Cookbook

How to do it…

In this recipe, we will be using ExpectedException as the JUnit rule because it helps the test declare that an exception is expected and also provides a way to clearly express the expected behavior. It is much more flexible than using the @Test(expected= ...) annotation because we can test specific error messages and custom fields.

In the following steps, we will learn how to write JUnit tests:

1. Let's first create a simple method that throws an exception. We will then write a test to test this method:

fun methodThrowsException() {    throw IllegalArgumentException("Age must be integer")}

2. Now, let's create a new rule of the ExpectedException class and write a test:

@Rulevar thrown = ExpectedException.none()@Testfun testExceptionFlow() ...