Expectation description

Enhance failures messages

Some expressions using matchers might not produce very useful messages. For example:

val ticketsNumber = 5

// will fail with '5' is not equal to '3'
ticketsNumber must be_==(3)

You can improve this failure message by describing what ticketsNumber represents:

val ticketsNumber = 5

// will fail with "the number of tickets '5' is not equal to '3'"
ticketsNumber aka "the number of tickets" must be_==(3)

The aka (also known as) method has a few variations:

• value.aka is a shortcut for value aka value.toString
• "a" post "is the first letter" prints a is the first letter
• "b" as ((s:String) => "a"+s+"c") prints abc
• Seq(1, 2, 3, 4).showAs((_:Seq[Int]).filter(isEven).mkString("|")) prints 2|4. This one is especially useful to filter out big data structures (lists, maps, xml…) before the displaying the failure message

Update the failure message

On a Matcher or a Result you can use updateMessage(f: String => String) or setMessage(m: String) to change the failure message.

Describe an expectation

Another way to provide a description for an expectation is to use the ==> (or <==>) operator:

s2"""A byname function can be transformed into a strict one $e1"""

def e1 = {
  def byNameFunction(u: =>Unit): Unit = {}
  var parameter = "not evaluated"
  toStrictFunction1(byNameFunction) { parameter = "evaluated" }

  "The byname function has become a strict one" ==> (parameter === "evaluated")
}

In the example above, testing if parameter == "evaluated" is just a way to observe what we wanted to achieve. If that doesn’t work, the failure message will be

[error] x The byname function has not become a strict one because 'evaluated' is not equal to 'not evaluated'