Clues

note

Clues only work if you are using the Kotest assertions library or Kotest test framework

Sometimes a failed assertion contains enough information in the error message to know what went wrong.

For example:

username shouldBe "sksamuel"

Might give an error like:

expected: "sksamuel" but was: "sam@myemailaddress.com"

And you would be able to see that you were populating the username field with an email address.

But let's say you had a test like this:

user.name shouldNotBe null

If this failed, you would simply get:

<null> should not equal <null>

Which isn't particularly helpful. This is where withClue comes into play.

The withClue and asClue helpers can add extra context to assertions so failures are self explanatory:

For example, we can use withClue with a string message

withClue("Name should be present") {
  user.name shouldNotBe null
}

Would give an error like this:

Name should be present
<null> should not equal <null>

We can also use the asClue extension function to turn any object into the clue message.

For example:

data class HttpResponse(val status: Int, val body: String)

val response = HttpResponse(404, "the content")

response.asClue {
    it.status shouldBe 200
    it.body shouldBe "the content"
}

Would output:

HttpResponse(status=404, body=the content)
Expected :200
Actual   :404