How to show custom failure messages in ScalaTest?

Question

Does anyone know how to show a custom failure message in ScalaTest?

For example:

NumberOfElements() should equal (5)

Shows the followin

Answer 1

You can also use withClue without importing anything or adding it to the test class:

withClue(s"Expecting distinct elements: ${elements.toList}") { elements.length shouldBe 3 }

This is imported from Assertions class: org.scalatest.Assertions#withClue