Testing Package-level function in kotlin which uses LocalDate

Question

I have DateUtil.kt file which contains.

fun getFirstDayOfTheWeek(): String {

    val firstDay: LocalDate = LocalDate.now(ZoneId.of(DateConstants.IST_ZONE_ID))
            .with(TemporalAdjusters.previousOrSame(DayOfWeek.MONDAY))
    return firstDay.toString()
}

How can i test this? There is no class and just functions. Using spring boot, @ExtendWith(SpringExtension.class) works at a class level.

Should i still create a DateUtilTest class for it , or is there a way to test without creating a class?

@ExtendWith(SpringExtension::class)
class DateUtilsTest {

    @Test
    fun getFirstDayOfTheWeekTest() {

    }
}

Also, Can someone help with how this function can be tested? Should i mock the LocalDate library?

Answer 1

You don't need SpringExtension to test simple non-spring code. All you need a simple test in a class.

Couple of things to consider while designing such function. LocalDate.now() makes the function impure. Instead this Date should come as a parameter to the function, so it is easier to test. With Kotlin, you can initialize with default value, so the signature does not change for function callers.

fun getFirstDayOfTheWeek(date: LocalDate = LocalDate.now()): String {

  val firstDay: LocalDate = date.with(TemporalAdjusters.previousOrSame(DayOfWeek.MONDAY))
  return firstDay.toString()
}

class DateUtilKt {

  @Test
  fun testFirstDayOfTheWeek() {
    val day = getFirstDayOfTheWeek(LocalDate.of(2020, 5,22))
    assertEquals("2020-05-18", day)
  }
}