How to mock scala readLine

Question

I want to write a unit test for my main function where there is a readLine() loop.

I have tried the following which is java based. I think readLine() might need System.in as inputStream. But it doesn't work. ScalaTest is blocked on the readLine() waiting for inputs.

"readLine" should "work" in {
  val in = new ByteArrayInputStream("abc".getBytes)
  System.setIn(in)
  readLine() === "tester"
}

Any ideas? Thank you.

Answer 1

The correct way to Unit Test it is to follow the "ports and adapters" pattern.

So you should have an interface that is the 'port' to the console reader so you could mock it in your unit test.

In addition you should have a Integration Test that verifies that your 'adapter' actually works against the real console.

According to the title of your question I guess you want to do an Integration test. You were almost there. You called a deprecated method that is deprecated since Scala 2.11.0. This code should work -

"readLine" should "work" in {
  val in = new ByteArrayInputStream("abc".getBytes)
  System.setIn(in)
  StdIn.readLine() === "abc"
}

Answer 2

Maxim's solution actually didn't work for me (anymore?). So to help others who face the same issue:

val in = new ByteArrayInputStream(("abc").getBytes)

Console.withIn(in)  {
    assert(StdIn.readLine() === "abc")
}