Fix test determinism

Author: sunkup

lib/src/test/kotlin/at/bitfire/synctools/mapping/tasks/builder/CompletedBuilderTest.kt

@@ -9,20 +9,24 @@ package at.bitfire.synctools.mapping.tasks.builder
 import android.content.ContentValues
 import android.content.Entity
 import androidx.core.content.contentValuesOf
+import at.bitfire.DefaultTimezoneRule
 import at.bitfire.ical4android.Task
 import at.bitfire.synctools.test.assertContentValuesEqual
 import net.fortuna.ical4j.model.property.Completed
 import org.dmfs.tasks.contract.TaskContract.Tasks
+import org.junit.Rule
 import org.junit.Test
 import org.junit.runner.RunWith
 import org.robolectric.RobolectricTestRunner
 import java.time.Instant
 import java.time.LocalDateTime
-import java.time.ZoneId
 
 @RunWith(RobolectricTestRunner::class)
 class CompletedBuilderTest {
 
+    @get:Rule
+    val tzRule = DefaultTimezoneRule("Europe/Berlin")
+
     private val builder = CompletedBuilder()
 
     @Test
@@ -63,7 +67,7 @@ class CompletedBuilderTest {
         )
         // floating date-time is interpreted in system default timezone
         val expectedTimestamp = LocalDateTime.of(2024, 6, 1, 12, 0, 0)
-            .atZone(ZoneId.systemDefault()).toInstant().epochSecond * 1000
+            .atZone(tzRule.defaultZoneId).toInstant().toEpochMilli()
         assertContentValuesEqual(contentValuesOf(
             Tasks.COMPLETED to expectedTimestamp,
             Tasks.COMPLETED_IS_ALLDAY to 0