diff --git a/Tests/NetworkingTests/Mocks/MockFileDataWriter.swift b/Tests/NetworkingTests/Mocks/MockFileDataWriter.swift
index ef65d81f..17c56c76 100644
--- a/Tests/NetworkingTests/Mocks/MockFileDataWriter.swift
+++ b/Tests/NetworkingTests/Mocks/MockFileDataWriter.swift
@@ -10,7 +10,7 @@ import Networking
 
 /// A test mock class for `FileDataWriting`.
 /// It writes into a file but let's us react when it's finished.
-class MockFileDataWriter: FileDataWriting {
+final class MockFileDataWriter: FileDataWriting {
     var writeClosure: (() -> Void)?
     private(set) var writeCalled = false
     private(set) var receivedData: Data?