import kotlin.test.*


private fun <T : Any> compareConversion(convertOrFail: (String) -> T,
                                        convertOrNull: (String) -> T?,
                                        equality: (T, T?) -> Boolean = { a, b -> a == b },
                                        assertions: ConversionContext<T>.() -> Unit) {
    ConversionContext(convertOrFail, convertOrNull, equality).assertions()
}

private class ConversionContext<T: Any>(val convertOrFail: (String) -> T,
                                        val convertOrNull: (String) -> T?,
                                        val equality: (T, T?) -> Boolean) {

    private fun assertEquals(expected: T, actual: T?, input: String, operation: String) {
        assertTrue(equality(expected, actual), "Expected $operation('$input') to produce $expected but was $actual")
    }

    fun assertProduces(input: String, output: T) {
        assertEquals(output, convertOrFail(input), input, "convertOrFail")
        assertEquals(output, convertOrNull(input), input, "convertOrNull")
    }

    fun assertFailsOrNull(input: String) {
        assertFailsWith<NumberFormatException>("Expected to fail on input \"$input\"") { convertOrFail(input) }
        assertNull(convertOrNull(input), message = "On input \"$input\"")
    }
}

fun box() {
    compareConversion({ it.toLong() }, { it.toLongOrNull() }) {
        assertProduces("٢٣١٩٦٠٧٧٨٤٥٩", 231960778459)
    }
}