diff --git a/Sources/Dependencies/DependencyValues/DefaultIsolation.swift b/Sources/Dependencies/DependencyValues/DefaultIsolation.swift
new file mode 100644
index 00000000..d4be56b1
--- /dev/null
+++ b/Sources/Dependencies/DependencyValues/DefaultIsolation.swift
@@ -0,0 +1,13 @@
+extension DependencyValues {
+  public var defaultIsolation: (any Actor)? {
+    get { self[DefaultIsolationKey.self] }
+    set { self[DefaultIsolationKey.self] = newValue }
+  }
+}
+
+private enum DefaultIsolationKey: DependencyKey {
+  public static var liveValue: (any Actor)? { nil }
+  public static var testValue: (any Actor)? { TestIsolation() }
+}
+
+private actor TestIsolation {}