Fix message backup checkout e2e tests.

core-util/src/main/java/org/signal/core/util/concurrent/SignalDispatchers.kt

@@ -0,0 +1,40 @@
+/*
+ * Copyright 2025 Signal Messenger, LLC
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+package org.signal.core.util.concurrent
+
+import kotlinx.coroutines.CoroutineDispatcher
+import kotlinx.coroutines.Dispatchers
+
+/**
+ * [Dispatchers] wrapper to allow tests to inject test dispatchers.
+ */
+object SignalDispatchers {
+
+  private var dispatcherProvider: DispatcherProvider = DefaultDispatcherProvider
+
+  fun setDispatcherProvider(dispatcherProvider: DispatcherProvider = DefaultDispatcherProvider) {
+    this.dispatcherProvider = dispatcherProvider
+  }
+
+  val Main get() = dispatcherProvider.main
+  val IO get() = dispatcherProvider.io
+  val Default get() = dispatcherProvider.default
+  val Unconfined get() = dispatcherProvider.unconfined
+
+  interface DispatcherProvider {
+    val main: CoroutineDispatcher
+    val io: CoroutineDispatcher
+    val default: CoroutineDispatcher
+    val unconfined: CoroutineDispatcher
+  }
+
+  private object DefaultDispatcherProvider : DispatcherProvider {
+    override val main: CoroutineDispatcher = Dispatchers.Main
+    override val io: CoroutineDispatcher = Dispatchers.IO
+    override val default: CoroutineDispatcher = Dispatchers.Default
+    override val unconfined: CoroutineDispatcher = Dispatchers.Unconfined
+  }
+}