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unit-testingjunitkotlinhamcrest
thecoshman
thecoshman

Reputation: 8650

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

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 get the following to compile?

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

Currently my IDE, InteliJ is highlighting that as a compilation error, saying it is expecting a ) after is?

Upvotes: 35

Views: 13481

Answers (3)

David Soroko
David Soroko

Reputation: 9086

You can alias is to Is (for example) in the import statement using the as keyword.

For example:

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

See https://kotlinlang.org/docs/packages.html#imports

Upvotes: 46

naXa stands with Ukraine
naXa stands with Ukraine

Reputation: 37916

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))

Upvotes: 17

thecoshman
thecoshman

Reputation: 8650

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))
  }
}

Upvotes: 42

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