Kotlin test, how to run BeforeEach with DescribeSpec test style

Question

I'm trying to write KotlinTest tests running on JUnit5, with the Describe Spec style.

When I need to initialize the same variable for some tests, @BeforeEach does not work inside DescribeSpec.

How can initialize data before each test?

class BlockchainUT : DescribeSpec({

    var blockchain = Blockchain()

    @BeforeEach
    fun beforeEach() {
        blockchain = Blockchain()
        blockchain.addBlock(listOf("foo1", "bar1"))
        blockchain.addBlock(listOf("foo2", "bar2"))
        blockchain.addBlock(listOf("foo3", "bar3"))
    }

    describe("isValidChain()") {

        context("when the chain does not start with the genesis block") {

            blockchain.chain[0] = Block(
                    System.currentTimeMillis(),
                    "---",
                    "xxx",
                    listOf("foo", "bar"))

            it("returns false") {
                Blockchain.isValid(blockchain) shouldBe false
            }
        }

        context("when the chain starts with the genesis block and has multiple blocks") {

            context("and a lastHash reference has changed returns false") {
                blockchain.chain[2] = Block(
                        blockchain.chain[2].timestamp,
                        "broken-lastHash",
                        blockchain.chain[2].hash,
                        blockchain.chain[2].data)
                it("returns false") {
                    Blockchain.isValid(blockchain) shouldBe false
                }
            }

            context("and the chain contains a block with an invalid field") {
                blockchain.chain[2] = Block(
                        blockchain.chain[2].timestamp,
                        blockchain.chain[2].lastHash,
                        blockchain.chain[2].hash,
                        listOf("some-bad-and-evil-data"))
                it("returns false") {
                    Blockchain.isValid(blockchain) shouldBe false
                }
            }
        }

    }
})

Answer 1

On the new version of KotlinTest 3.3 there are new Listeners to define beforeTest, afterTest, beforeSpec and so on.

In this case a posible solution should be:

class BlockchainUT : DescribeSpec(), TestListener {

    var blockchain = Blockchain()

    override fun beforeTest(describe: TestCase): Unit {
        blockchain = Blockchain()
        blockchain.addBlock(listOf("foo1", "bar1"))
        blockchain.addBlock(listOf("foo2", "bar2"))
        blockchain.addBlock(listOf("foo3", "bar3"))
    }

    init {
        describe("isValidChain()") {

            context("when the chain starts with the genesis block and has multiple blocks") {

                context("and a lastHash reference has changed returns false") {

                    blockchain.chain[2] = Block(
                            blockchain.chain[2].timestamp,
                            "broken-lastHash",
                            blockchain.chain[2].hash,
                            blockchain.chain[2].data)

                    it("returns false") {
                        Blockchain.isValid(blockchain) shouldBe false
                    }
                }

                context("and the chain contains a block with an invalid field") {

                    blockchain.chain[2] = Block(
                            blockchain.chain[2].timestamp,
                            blockchain.chain[2].lastHash,
                            blockchain.chain[2].hash,
                            listOf("some-bad-and-evil-data"))

                    it("returns false") {
                        Blockchain.isValid(blockchain) shouldBe false
                    }
                }

                context("and the chain does not contain any invalid blocks") {

                    it("returns true") {
                        Blockchain.isValid(blockchain) shouldBe true
                    }
                }
            }
        }
    }
}

Also can be solved using the new Isolation Modes, defining the isolation mode to InstancePerLeaf. From io.kotlintest.IsolationMode javadoc:

A new instance of the [Spec] class is instantiated for every
[TestCase] - both containers and leaf tests - and they are
executed once the previous test has completed.
For example, in the following test plan:
"this test" {
  println("a")
  "nested test" {
    println("b")
  }
  "nested test 2" {
    println("c")
  }
}
The output will be:
a
a
b
a
c

3. And finally move the code you want to repeat for every [TestCase]

class BlockchainUT : DescribeSpec(){

    override fun isolationMode() = IsolationMode.InstancePerTest

        describe("isValidChain()") {

            context("when the chain starts with the genesis block and has multiple blocks") {

                var blockchain = Blockchain()
                blockchain.addBlock(listOf("foo1", "bar1"))
                blockchain.addBlock(listOf("foo2", "bar2"))
                blockchain.addBlock(listOf("foo3", "bar3"))

                context("and a lastHash reference has changed returns false") {

                    blockchain.chain[2] = Block(
                            blockchain.chain[2].timestamp,
                            "broken-lastHash",
                            blockchain.chain[2].hash,
                            blockchain.chain[2].data)

                    it("returns false") {
                        Blockchain.isValid(blockchain) shouldBe false
                    }
                }

                context("and the chain contains a block with an invalid field") {

                    blockchain.chain[2] = Block(
                            blockchain.chain[2].timestamp,
                            blockchain.chain[2].lastHash,
                            blockchain.chain[2].hash,
                            listOf("some-bad-and-evil-data"))

                    it("returns false") {
                        Blockchain.isValid(blockchain) shouldBe false
                    }
                }

                context("and the chain does not contain any invalid blocks") {

                    it("returns true") {
                        Blockchain.isValid(blockchain) shouldBe true
                    }
                }
            }
        }
    }
}