Add unit testing for pinned last message deletion fix.

app/src/androidTest/java/org/thoughtcrime/securesms/testing/SignalDatabaseRule.kt

@@ -0,0 +1,40 @@
+package org.thoughtcrime.securesms.testing
+
+import org.junit.rules.TestWatcher
+import org.junit.runner.Description
+import org.thoughtcrime.securesms.database.SignalDatabase
+import org.thoughtcrime.securesms.keyvalue.SignalStore
+import org.whispersystems.signalservice.api.push.ACI
+import org.whispersystems.signalservice.api.push.PNI
+import java.util.UUID
+
+/**
+ * Sets up bare-minimum to allow writing unit tests against the database,
+ * including setting up the local ACI and PNI pair.
+ *
+ * @param deleteAllThreadsOnEachRun Run deleteAllThreads between each unit test
+ */
+class SignalDatabaseRule(
+  private val deleteAllThreadsOnEachRun: Boolean = true
+) : TestWatcher() {
+
+  val localAci: ACI = ACI.from(UUID.randomUUID())
+  val localPni: PNI = PNI.from(UUID.randomUUID())
+
+  override fun starting(description: Description?) {
+    deleteAllThreads()
+
+    SignalStore.account().setAci(localAci)
+    SignalStore.account().setPni(localPni)
+  }
+
+  override fun finished(description: Description?) {
+    deleteAllThreads()
+  }
+
+  private fun deleteAllThreads() {
+    if (deleteAllThreadsOnEachRun) {
+      SignalDatabase.mms.deleteAllThreads()
+    }
+  }
+}