Dynamic Test Generation

Tests in ZIO are dynamic. Meaning that they are not required to be statically defined at compile time. They can be generated at runtime effectfully.

Assume we have implemented the add operator which adds two numbers:

def add(a: Int, b: Int): Int = ???

We want to test this function using the following test data inside the resources directory:

src/test/resources/test-data.csv

0, 0, 0
1, 0, 1
0, 1, 1
0, -1, -1
-1, 0, -1
1, 1, 2
1, -1, 0
-1, 1, 0

Let's load it and create a bunch of tests using this test data:

import zio._
import zio.test._
import zio.test.test

def loadTestData: Task[List[((Int, Int), Int)]] =
  ZIO.attemptBlocking(
    scala.io.Source
      .fromResource("test-data.csv")
      .getLines()
      .toList
      .map(_.split(',').map(_.trim))
      .map(i => ((i(0).toInt, i(1).toInt), i(2).toInt))
  )
  
def makeTest(a: Int, b: Int)(expected: Int): Spec[Any, Nothing] =
  test(s"test add($a, $b) == $expected") {
    assertTrue(add(a, b) == expected)
  }

def makeTests: ZIO[Any, Throwable, List[Spec[Any, Nothing]]] =
  loadTestData.map { testData =>
    testData.map { case ((a, b), expected) =>
      makeTest(a, b)(expected)
    }
  }

Now we are ready to run all generated tests:

import zio._
import zio.test._

object AdditionSpec extends ZIOSpecDefault {
  override def spec = suite("add")(makeTests)
}

Here is the test runner's output:

+ add
  + test add(0, 0) == 0
  + test add(1, 0) == 1
  + test add(0, -1) == -1
  + test add(0, 1) == 1
  + test add(-1, 1) == 0
  + test add(1, -1) == 0
  + test add(1, 1) == 2
  + test add(-1, 0) == -1
8 tests passed. 0 tests failed. 0 tests ignored.