feat: 입력된 날짜 기준 지난 주 일요일을 찾는 유틸 및 테스트 추가

src/main/kotlin/roomescape/common/util/DateUtils.kt

@@ -0,0 +1,11 @@
+package roomescape.common.util
+
+import java.time.DayOfWeek
+import java.time.LocalDate
+import java.time.temporal.TemporalAdjusters
+
+object DateUtils {
+    fun getSundayOfPreviousWeek(date: LocalDate): LocalDate = date
+        .minusWeeks(1)
+        .with(TemporalAdjusters.previousOrSame(DayOfWeek.SUNDAY))
+}

src/test/kotlin/roomescape/common/util/DateUtilsTest.kt

@@ -0,0 +1,15 @@
+package roomescape.common.util
+
+import io.kotest.core.spec.style.StringSpec
+import io.kotest.matchers.shouldBe
+import java.time.LocalDate
+
+class DateUtilsTest : StringSpec({
+    "입력된 날짜의 이전 주 일요일을 찾는다." {
+        val expected = LocalDate.of(2025, 8, 31)
+
+        for (i in 7..13){
+            DateUtils.getSundayOfPreviousWeek(LocalDate.of(2025, 9, i)) shouldBe expected
+        }
+    }
+})