Mockk equality matcher that uses reflection to verify equality of two objects. Useful when testing objects that don't offer an equals() method. Requires org.apache.commons

ReflectedEqualityMatcher.kt

import io.mockk.Matcher
import io.mockk.MockKMatcherScope
import org.apache.commons.lang3.builder.EqualsBuilder

class ReflectedEqualityMatcher<T>(
    private val expected: T
) : Matcher<T> {

    override fun match(arg: T?): Boolean {
        if (arg == null) {
            return false
        }

        return EqualsBuilder()
            .setTestRecursive(true)
            .setTestTransients(true)
            .reflectionAppend(expected, arg)
            .isEquals
    }
}

inline fun <reified T : Any> MockKMatcherScope.reflectedEq(expected: T): T = match(ReflectedEqualityMatcher(expected))

// Example usage
val expected = XYZ()
verify { someService.doSomething(reflectedEq(expected)) }

// Unit tests
class ReflectedEqualityMatcherTest {

    @Test
    fun `given two objects with differing values, when matching, should not match objects`() {
        val expected = ComparisonStub(field = "123", anotherField = "456")
        val actual = ComparisonStub(field = "123", anotherField = "912")

        val matcher = ReflectedEqualityMatcher(expected)

        assert(matcher.match(actual)).isFalse()
    }

    @Test
    fun `given two objects with same values, when matching, should match objects`() {
        val expected = ComparisonStub(field = "123", anotherField = "456")
        val actual = ComparisonStub(field = "123", anotherField = "456")

        val matcher = ReflectedEqualityMatcher(expected)

        assert(matcher.match(actual)).isTrue()
    }

    @Test
    fun `given two objects with differing values in nested field, when matching, should not match objects`() {
        val expected = NestedComparisonStub(ComparisonStub(field = "123", anotherField = "456"))
        val actual = NestedComparisonStub(ComparisonStub(field = "abc", anotherField = "456"))

        val matcher = ReflectedEqualityMatcher(expected)

        assert(matcher.match(actual)).isFalse()
    }

    @Test
    fun `given two objects with same values in nested field, when matching, should match objects`() {
        val expected = NestedComparisonStub(ComparisonStub(field = "123", anotherField = "456"))
        val actual = NestedComparisonStub(ComparisonStub(field = "123", anotherField = "456"))

        val matcher = ReflectedEqualityMatcher(expected)

        assert(matcher.match(actual)).isTrue()
    }

    private class ComparisonStub(
        private val field: String,
        val anotherField: String
    )

    private class NestedComparisonStub(
        private val nestedClass: ComparisonStub
    )
}