Spek: Attempting to memoize System.out causes test to not run.

[snowe2010]

I'm unsure of how to actually describe this, but if I attempt to memoize something like

val originalOut by memoized<PrintStream>()
...
val originalOut by memoize { System.out }

the test fails to run in intellij, this is what it looks like

[jcornaz]

Very strange indeed.

However it doesn't seam to happen in memoize but when System.setOut is called.

Here is a minimal reproducer:

object MemoizedStreamSpec : Spek({
  describe("System.setOut") {
    it("should replace standard output stream") {
      val baos = ByteArrayOutputStream()

      System.setOut(PrintStream(baos))

      print("Hello world")

      assertEquals("Hello world", String(baos.toByteArray()))
    }
  }
})

EDIT: It is only a problem of the IntellIJ plugin. Running the test from gradle pass as expected.

[snowe2010]

@jcornaz it doesn't work for you without the memoization? That's weird because for me if I leave it as

fun Root.setupStreams() {
    val outContent by memoized<ByteArrayOutputStream>()
    val errContent by memoized<ByteArrayOutputStream>()
    val originalOut = System.out
    val originalErr = System.err

    // Create new byte stream for each test
    beforeEachTest {
        System.setOut(PrintStream(outContent))
        System.setErr(PrintStream(errContent))
    }
    afterEachTest {
        System.setOut(originalOut)
        System.setErr(originalErr)
    }
}

it works fine.

[raniejade]

I may know what the problem is. When tests are run within IJ a new processed is spawned with stdout and stderr captured; this is used to communicate the test run events to IJ. So my guess is since you are overriding the default print streams - IJ is not receiving any events. Is there a way for you not to write directly to System.out and System.err? Maybe some variables which default to System.out and System.err - but you override them on the tests.

[snowe2010]

Hmm. well the whole point of my project is to print stuff to console. I'm not sure of another way to test it 😢. I guess I could rewrite my function to not use println but instead use a writer and write straight to PrintStream and then mock that in some way, though I tried mocking PrintStream once and it didn't work.

Anyway, if this isn't actually related to spek then we can close it. Sorry for the bother.

[raniejade]

I was thinking something like this:

// top level fields
internal var sysout= System.out
internal var syserr = System.err

Instead of using print do sysout.print(...). Then on your tests just override the value of sysout and syserr (probably in setupStreams).

sysout = PrintStream(...)
syserr = PrintStream(...)

Relying on System.out and System.err makes your test very brittle, as anyone can override the value at any given time. Also, a rouge print call from another thread can cause your tests to fail.