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Version: 5.2



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: ""

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: 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") { 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