Classic Assertions

note

In almost all cases we encourage developers using smart assertions instead of classic assertions. They are more expressive and easier to use. So you can skip reading this section.

Only use classic assertions when you know what you are doing. There are some rare cases where the smart assertions are not enough.

The assert and its effectful counterpart assertZIO are the old way of asserting ordinary values and ZIO effects.

Asserting Ordinary Values

In order to test ordinary values, we should use assert, like the example below:

import zio._
import zio.test.{test, _}

test("sum") {
  assert(1 + 1)(Assertion.equalTo(2))
}

Asserting ZIO Effects

If we are testing an effect, we should use the assertZIO function:

import zio._
import zio.test.{test, _}

test("updating ref") {
  val value = for {
    r <- Ref.make(0)
    _ <- r.update(_ + 1)
    v <- r.get
  } yield v
  assertZIO(value)(Assertion.equalTo(1))
}

The for-comprehension Style

Having this all in mind, probably the most common and also most readable way of structuring tests is to pass a for-comprehension to test function and yield a call to assert function.

import zio._
import zio.test.{test, _}

test("updating ref") {
  for {
    r <- Ref.make(0)
    _ <- r.update(_ + 1)
    v <- r.get
  } yield assert(v)(Assertion.equalTo(v))
}