Kotest Inspectors

In addition to matchers, Kotest supports inspectors, extension functions for collections that verify whether an assertion holds for a particular group of elements.

Inspectors

Inspectors are extension functions for collections and arrays. They verify whether the given assertion is true for a specified number or group of elements.

For example, the following verifies that at least two values in xs are greater than zero.

xs.forAtLeast(2) {
    it shouldBeGreaterThan 0
}

The following verifies that no element in xs is greater than zero.

xs.forNone {
    it shouldBeGreaterThan 0
}

Kotest provides these inspectors:

Inspector	Description
`forAll`	The assertion must pass for every element.
`forNone`	The assertion must fail for every element.
`forOne`	The assertion must pass for exactly one element.
`forAtMostOne`	The assertion must pass for at most one element.
`forAtLeastOne`	The assertion must pass for at least one element.
`forAtLeast(k)`	The assertion must pass for at least `k` elements.
`forAtMost(k)`	The assertion must pass for at most `k` elements.
`forAny`	Alias for `forAtLeastOne`.
`forSome`	The assertion must pass for at least one element but not all elements.
`forExactly(k)`	The assertion must pass for exactly `k` elements.

Example:

import io.kotest.core.spec.style.FunSpec
import io.kotest.inspectors.forAll
import io.kotest.inspectors.forAtLeast
import io.kotest.inspectors.forNone
import io.kotest.matchers.ints.shouldBeGreaterThan

class NumbersTestWithInspectors : FunSpec({
    test("inspectors") {
        val numbers = listOf(1, 2, 3, 4, 5)

        numbers.forAll {
            it shouldBeGreaterThan 0
        }

        numbers.forAtLeast(2) {
            it shouldBeGreaterThan 3
        }

        numbers.forNone {
            it shouldBeGreaterThan 10
        }
    }
})

References

Inspectors | Kotest