Understanding test suites

Question

I'm learning scalatest and have a question about suites. I want to test a

class ByteSource(val src: Array[Byte])

And logically I splitted the test cases into the following two:

1. Empty byte source
2. Non empty byte source

The question is if it's correct to split the cases into different suites like this:

class ByteSourceTest extends FunSpec with Matchers{
    describe("empty byte source operations"){
        //...
    }

    describe("non-empty byte source operations"){
        //...
    }
}

Or FunSpec is not quite suitable for such a case?

Answer 1

FunSpec is designed to provide minimal structure so there are no hard rules here. An example of opinionated structure would be WordSpec. One suggestion I would make is to clearly identity the subject of your test by having an outer describe("A ByteSource"):

class ByteSourceTest extends FunSpec with Matchers {
  describe("A ByteSource") {
    describe("when empty") {
      val byteSource = new ByteSource(new Array[Byte](0))

      it("should have size 0") {
        assert(byteSource.src.size == 0)
      }

      it("should produce NoSuchElementException when head is invoked") {
        assertThrows[NoSuchElementException] {
          byteSource.src.head
        }
      }
    }

    describe("when non-empty") {
      val byteSource = new ByteSource(new Array[Byte](10))

      it("should have size > 0") {
        assert(byteSource.src.size > 0)
      }

      it("should not produce NoSuchElementException when head is invoked") {
        noException shouldBe thrownBy {
          byteSource.src.head
        }
      }
    }
  }
}

Having test subject the output seems to read like a specification in natural language:

A ByteSource
  when empty
  - should have size 0
  - should produce NoSuchElementException when head is invoked
  when non-empty
  - should have size > 0
  - should not produce NoSuchElementException when head is invoked