How can I test a scala function? - scala

Question

I started learning scala and in order to learn, I want to play with some functions. However, I dont know how to make a functions return value appear on the console. I am using sbt.
I tried with return and Console.println, I guess I dont use it right.
for example:
def func(ls: List[Boolean]): Boolean = ls match
{
case Nil => false
case l::ls => l != func(ls)
}
how do I see what this function returns?

Answer 1

Scastie is an online interactive playground for Scala and is a quick way to get started. For example, pasting the following in the editor and pressing Save button
def func(ls: List[Boolean]): Boolean = ls match {
case Nil => false
case l::ls => l != func(ls)
}
func(List(true, false, true))
should evaluate func and show the result inline like so
func(List(true, false, true)) // false: Boolean
Also try println(func(List(true, false, true)))
Another way of testing the expected result without having to print it is to use assertions like so
assert(func(List(true, false, true)) == false)
To convert above assertion to a real unit test we could instantiate an application from Scala Giter8 template like so
sbt new scala/scala-seed.g8
which setups all the furniture necessary to quickly run and test applications. Then add func to src/main/scala/example/Hello.scala like so
object Hello extends App {
def func(ls: List[Boolean]): Boolean = ls match {
case Nil => false
case l::ls => l != func(ls)
}
}
and add corresponding unit tests to src/test/scala/example/HelloSpec.scala like so
class HelloSpec extends FlatSpec with Matchers {
"func" should "return false on List(true, false, true)" in {
Hello.func(List(true, false, true)) shouldEqual false
}
it should "return false on empty list" in {
Hello.func(List()) shouldEqual false
}
// add further tests here
}
Now executing sbt test should output
[info] HelloSpec:
[info] func
[info] - should return false on List(true, false, true)
[info] - should return false on empty list
[info] Run completed in 127 milliseconds.
[info] Total number of tests run: 2
[info] Suites: completed 1, aborted 0
[info] Tests: succeeded 2, failed 0, canceled 0, ignored 0, pending 0
[info] All tests passed.

Answer 2

You can try this:
scala> :paste
// Entering paste mode (ctrl-D to finish)
def func(ls: List[Boolean]): Boolean = ls match
{
case Nil => false
case l::ls => l != func(ls)
}
// Exiting paste mode, now interpreting.
func: (ls: List[Boolean])Boolean
scala> func(List(true, false, true))
res0: Boolean = false