Testing Program Who Having PrintLn Output - scala

Question

I having problem with program which is prints to standard outputs. The method I test is print to standard output so it having Unit return type. I then writing Scalatest to assert output but I don't know how. I get error like this
This is output of Scalatest
Customer 1 : 20.0
Customer 2 : 20.0
Customer 3 : 20.0
Customer 4 : 20.0
Customer 5 : 20.0
<(), the Unit value> did not equal "Customer 1 : 20.0
Customer 2 : 20.0
Customer 3 : 20.0
Customer 4 : 20.0
Customer 5 : 20.0"
My assert looking like
assert(output() == "Customer 1 : 20.0\nCustomer 2 : 20.0\nCustomer 3 : 20.0\nCustomer 4 : 20.0\nCustomer 5 : 20.0")
How can I testing this?

Answer 1

Console.withOut enables temporary redirection of output to a stream that we can assert on, for example,
class OutputSpec extends FlatSpec with Matchers {
val someStr =
"""
|Customer 1 : 20.0
|Customer 2 : 20.0
|Customer 3 : 20.0
|Customer 4 : 20.0
|Customer 5 : 20.0
""".stripMargin
def output(): Unit = println(someStr)
"Output" should "print customer information" in {
val stream = new java.io.ByteArrayOutputStream()
Console.withOut(stream) { output() }
assert(stream.toString contains someStr)
}
}