Test TimeZone.currentSystemDefault() = ZoneId.system() on JS without tzdb

Author: dkhalanskyjb

js-without-timezones/common/test/JSJoda.module_@js-joda_core.kt

@@ -0,0 +1,34 @@
+/*
+ * Copyright 2019-2024 JetBrains s.r.o. and contributors.
+ * Use of this source code is governed by the Apache 2.0 License that can be found in the LICENSE.txt file.
+ */
+@file:JsModule("@js-joda/core")
+@file:JsNonModule
+package kotlinx.datetime.test.JSJoda
+
+import kotlinx.datetime.internal.InteropInterface
+import kotlinx.datetime.internal.JsModule
+import kotlinx.datetime.internal.JsNonModule
+
+external class ZonedDateTime : InteropInterface {
+    fun year(): Int
+    fun monthValue(): Int
+    fun dayOfMonth(): Int
+    fun hour(): Int
+    fun minute(): Int
+    fun second(): Int
+    fun nano(): Double
+}
+
+external class Instant : InteropInterface {
+    fun atZone(zone: ZoneId): ZonedDateTime
+    companion object {
+        fun ofEpochMilli(epochMilli: Double): Instant
+    }
+}
+
+external class ZoneId : InteropInterface {
+    companion object {
+        fun systemDefault(): ZoneId
+    }
+}

js-without-timezones/common/test/TimezonesWithoutDatabaseTest.kt

@@ -7,6 +7,8 @@ package kotlinx.datetime.test
 
 import kotlinx.datetime.*
 import kotlin.test.*
+import kotlinx.datetime.test.JSJoda.ZoneId as jtZoneId
+import kotlinx.datetime.test.JSJoda.Instant as jtInstant
 
 class TimezonesWithoutDatabaseTest {
     @Test
@@ -25,6 +27,28 @@ class TimezonesWithoutDatabaseTest {
         assertEquals(today.atTime(0, 0).toInstant(tz), today.atStartOfDayIn(tz))
     }
 
+    @Test
+    fun systemSameAsJoda() {
+        val tz = TimeZone.currentSystemDefault()
+        val jodaTz = jtZoneId.systemDefault()
+        assertEquals(jodaTz.toString(), tz.id)
+        val range = Instant.DISTANT_PAST.toEpochMilliseconds()..Instant.DISTANT_FUTURE.toEpochMilliseconds()
+        repeat(1000) {
+            val epochMilli = range.random()
+            val instant = Instant.fromEpochMilliseconds(epochMilli)
+            val jodaInstant = jtInstant.ofEpochMilli(epochMilli.toDouble())
+            val localDateTime = instant.toLocalDateTime(tz)
+            val jodaLocalDateTime = jodaInstant.atZone(jodaTz)
+            assertEquals(jodaLocalDateTime.year(), localDateTime.year)
+            assertEquals(jodaLocalDateTime.monthValue(), localDateTime.monthNumber)
+            assertEquals(jodaLocalDateTime.dayOfMonth(), localDateTime.dayOfMonth)
+            assertEquals(jodaLocalDateTime.hour(), localDateTime.hour)
+            assertEquals(jodaLocalDateTime.minute(), localDateTime.minute)
+            assertEquals(jodaLocalDateTime.second(), localDateTime.second)
+            assertEquals(jodaLocalDateTime.nano(), localDateTime.nanosecond.toDouble())
+        }
+    }
+
     @Test
     fun utc() {
         val utc: FixedOffsetTimeZone = TimeZone.UTC