kotlin.test — Basic Tests

// build.gradle.kts:
//   testImplementation(kotlin("test"))

import kotlin.test.*

class Calculator {
    fun add(a: Int, b: Int) = a + b
    fun divide(a: Int, b: Int): Int {
        require(b != 0) { "divide by zero" }
        return a / b
    }
}

class CalculatorTest {
    private val calc = Calculator()

    @Test
    fun adds_two_positive_numbers() {
        assertEquals(5, calc.add(2, 3))
    }

    @Test
    fun throws_on_divide_by_zero() {
        val ex = assertFailsWith<IllegalArgumentException> {
            calc.divide(10, 0)
        }
        assertEquals("divide by zero", ex.message)
    }

    @Test
    fun assertions_we_use_often() {
        assertEquals(4, calc.add(2, 2))
        assertNotEquals(0, calc.add(1, 1))
        assertTrue(calc.add(1, 1) > 0)
        assertFalse(calc.add(0, 0) > 0)
        assertNull(emptyList<Int>().firstOrNull())
        assertNotNull(calc.divide(10, 2))
    }
}