Kotlin for assertThat(foo, instanceOf(Bar.class))

Question

How would you write assertThat(foo, instanceOf(Bar.class)) with Kotlin?

Seems that it does not like the .class

I would like to go for an assertion which is a bit more "precise" than just an assertTrue(foo is Bar) if possible

Answer 1

Bar::class returns instance of KClass, which is Kotlin equivalent of Java's Class.

instanceOf method requires Class instance, not KClass, so you have to convert it using Bar::class.java.

So your assertion should be like:

assertThat(foo, instanceOf(Bar::class.java))

More info about Java interop you can find here.

Also you can have a look at Hamkrest library which may add more fluency to your assertions:

assert.that(foo, isA<Bar>())

Answer 2

You could use Atrium (https://atriumlib.org) and write the following

assertThat(foo).isA<Bar>{} 

And in case you want to assert more about foo, say Bar has a val baz: Int, then you can write the following

assertThat(foo).isA<Bar> { 
  property(subject::baz).isSmallerThan(41) 
}