Using EitherValues
ScalaTest's EitherValues trait provides an implicit conversion that adds left.value and right.value methods
to Either, which will return the selected value of the Either if defined,
or throw TestFailedException if not.
This construct allows you to express in one statement that an Either should be left or right
and that its value should meet some expectation. Here's are some examples:
either1.right.value should be > 9
either2.left.value should be ("Muchas problemas")
Or, using assertions instead of matcher expressions:
assert(either1.right.value > 9)
assert(either2.left.value === "Muchas problemas")
Were you to simply invoke right.get or left.get on the Either,
if the Either wasn't defined as expected (e.g., it was a Left when you expected a Right), it
would throw a NoSuchElementException:
val either: Either[String, Int] = Left("Muchas problemas")
either.right.get should be > 9
The NoSuchElementException would cause the test to fail, but without providing a stack depth pointing
to the failing line of test code. This stack depth, provided by TestFailedException (and a
few other ScalaTest exceptions), makes it quicker for
users to navigate to the cause of the failure. Without EitherValues, to get
a stack depth exception you would need to make two statements, like this:
val either: Either[String, Int] = Left("Muchas problemas")
either should be ('right)
either.right.get should be > 9
The EitherValues trait allows you to state that more concisely:
val either: Either[String, Int] = Left("Muchas problemas")
either.right.value should be > 9
Next, we can look at another goodie. Let's learn about using PartialFunctionValues.
