How to compile Kotlin unit test code that uses hamcrest 'is'

Question

I want to write a unit test for my Kotlin code and use junit/hamcrest matchers, I want to use the is method, but it is a reserved word in Kotlin.

How can I

Answer 1

As others pointed out, in Kotlin, is is a reserved word (see Type Checks). But it's not a big problem with Hamcrest since is function is just a decorator. It's used for better code readability, but it's not required for proper functioning.

You are free to use a shorter Kotlin-friendly expression.

1. equality:

   assertThat(cheese, equalTo(smelly))
   

   instead of:

   assertThat(cheese, `is`(equalTo(smelly)))
   

2. matcher decorator:

   assertThat(cheeseBasket, empty())
   

   instead of:

   assertThat(cheeseBasket, `is`(empty()))
   

Another frequently used Hamcrest matcher is a type-check like

assertThat(cheese, `is`(Cheddar.class))

It's deprecated and it's not Kotlin-friendly. Instead, you're advised to use one of the following:

assertThat(cheese, isA(Cheddar.class))
assertThat(cheese, instanceOf(Cheddar.class))

Answer 2

You can alias is (say to Is) when you import, using the as keyword.

E.g:

 import org.hamcrest.CoreMatchers.`is` as Is

See https://kotlinlang.org/docs/reference/packages.html

Answer 3

In Kotlin, is is a reserved word . To get around this you need to escape the code using backticks, so the following will allow you to compile the code:

class testExample{
  @Test fun example(){
    assertThat(1, `is`(equalTo(1))
  }
}