test(reminders): cover disabled-calendar alert filtering

Extract the disabled-calendar filtering from EventReminderReceiver into a
pure postableAlerts() function and unit-test it, since the receiver flow
itself is not reachable from a plain JUnit test.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

app/src/test/java/de/jeanlucmakiola/calendula/data/reminders/PostableAlertsTest.kt

@@ -0,0 +1,55 @@
+package de.jeanlucmakiola.calendula.data.reminders
+
+import com.google.common.truth.Truth.assertThat
+import org.junit.jupiter.api.Test
+
+class PostableAlertsTest {
+
+    private fun alert(alertId: Long, calendarId: Long) = ReminderAlert(
+        alertId = alertId,
+        eventId = alertId * 10,
+        calendarId = calendarId,
+        beginMillis = 0L,
+        endMillis = 0L,
+        title = "Event $alertId",
+        location = null,
+        isAllDay = false,
+    )
+
+    @Test
+    fun `keeps alerts when no calendar is disabled`() {
+        val due = listOf(alert(1, calendarId = 100), alert(2, calendarId = 200))
+
+        val postable = postableAlerts(due, disabledCalendarIds = emptySet())
+
+        assertThat(postable).isEqualTo(due)
+    }
+
+    @Test
+    fun `drops alerts for a disabled calendar`() {
+        val keep = alert(1, calendarId = 100)
+        val drop = alert(2, calendarId = 200)
+
+        val postable = postableAlerts(listOf(keep, drop), disabledCalendarIds = setOf(200))
+
+        assertThat(postable).containsExactly(keep)
+    }
+
+    @Test
+    fun `drops every alert when all their calendars are disabled`() {
+        val due = listOf(alert(1, calendarId = 100), alert(2, calendarId = 100))
+
+        val postable = postableAlerts(due, disabledCalendarIds = setOf(100))
+
+        assertThat(postable).isEmpty()
+    }
+
+    @Test
+    fun `keeps multiple alerts from the same enabled calendar`() {
+        val due = listOf(alert(1, calendarId = 100), alert(2, calendarId = 100))
+
+        val postable = postableAlerts(due, disabledCalendarIds = setOf(999))
+
+        assertThat(postable).isEqualTo(due)
+    }
+}