Assertion shouldBe succeeds even when equals() always returns false

Here’s a simple class that implements a Set interface and always returns false from its equals() method. That should mean that every shouldBe assertion fails, right?

In my case, using kotest 5.1.0, first two tests succeed, and the last one fails - it seems kotest is doing something else instead of using the equals() method.

Is this a bug, or just unexpected behavior? If so, is there an assertion that always uses the equals() method?

class ArraySet(vararg items: String) : Set<String> {

    private val items: Array<String> = items.distinct().toTypedArray()

    override val size get() = items.size
    override fun iterator() = items.iterator()
    override fun contains(element: String) = items.contains(element)
    override fun containsAll(elements: Collection<String>) = items.toList().containsAll(elements)
    override fun isEmpty() = items.isEmpty()

    override fun equals(other: Any?): Boolean = false

    override fun hashCode(): Int {
        return items.sumOf { it.hashCode() }
    }
}

class ArraySetTest : FunSpec({
    val o1 = ArraySet("foo", "bar")
    val o2 = ArraySet("bar", "foo")
    val o3 = ArraySet("foo", "bar")
    val o4 = ArraySet("foo, bar, baz")

    test("1. equal up to permutation") {
        o1 shouldBe o2
    }
    test("2. completely equal") {
        o1 shouldBe o3
    }
    test("3. different elements") {
        o1 shouldBe o4
    }
})

[sksamuel]

I think shouldBe should (and does) use equals except where we override it for special behavior - like we are doing for sets for example.

This example is failing because I think we are using the iterator methods of set, and thus not the equals behavior. We should document all the special cases for shouldBe. And after that I can add lint rules to the kotest plugin to warn you.

[LeoColman]

There is the EqualityMatcher already, I think we’re just missing the infix functions

kotest-assertions/kotest-assertions-shared/src/commonMain/kotlin/io/kotest/assertions/eq/DefaultEq.kt:14

This is the default equality matcher, it uses ==