Operations

Logical Operations

What is really useful in assertions is that they behave like boolean values and can be composed with operators known from operating on boolean values like and (&&), or (||), negation (negate):

import zio.test.Assertion

val assertionForString: Assertion[String] = 
  Assertion.containsString("Foo") && Assertion.endsWithString("Bar")

Composable Nested Assertions

Assertions also compose with each other allowing for doing rich diffs not only simple value to value comparison:

import zio.test._
import zio.test.Assertion.{isRight, isSome, equalTo, hasField}

test("Check assertions") {
  assert(Right(Some(2)))(isRight(isSome(equalTo(2))))
}

Here we're checking deeply nested values inside an Either and Option. Because Assertions compose this is not a problem. All layers are being peeled off tested for the condition until the final value is reached.

Here the expression Right(Some(2)) is of type Either[Any, Option[Int]] and our assertion isRight(isSome(equalTo(2))) is of type Assertion[Either[Any, Option[Int]]]