Troubleshooting “Undefined symbols for architecture x86_64” Error in Swift UITests

Troubleshooting "Undefined symbols for architecture x86_64" Error in Swift UITests

11 April 2024 Stephan Petzl Leave a comment Tech-Help

Developers often encounter various errors when running unit tests and UI tests in Swift, one of which is the “Undefined symbols for architecture x86_64” error. This article aims to shed light on the nature of this error and provide guidance on how to approach it.

Understanding the Error

When you see an error message that includes “Undefined symbols for architecture x86_64”, it indicates that the linker is unable to find the definitions for the referenced symbols in your Swift project. This can occur in a testing environment, particularly when setting up UI tests.

For instance, you might encounter this error when trying to access a Swift string constant from within a UI test class:

                Undefined symbols for architecture x86_64:
  "DirectBistro.DBTabBarOrderedIndexesKey.unsafeMutableAddressor : Swift.String", referenced from:
      DirectBistroUITests.TabBarControllerTests.setUp (DirectBistroUITests.TabBarControllerTests)() -> () in TabBarControllerTests.o
ld: symbol(s) not found for architecture x86_64

Addressing the Issue

It’s important to recognize the distinction between unit tests and UI tests within the context of Swift testing:

  • Unit Tests: These tests run inside your application process and can access your application code directly.
  • UI Tests: These tests run in a separate process, outside of your application, to simulate user interactions. UI tests are not expected to access app classes or internal code directly.

With this understanding, when you encounter the aforementioned error during UI testing, it is indicative of an attempt to access application code in a manner that is not supported by UI tests.

When writing UI tests, you should avoid direct access to the application’s internal code or state. Instead, UI tests should interact with the app as a user would, through the UI elements exposed by the application.

If you need to set up the application state for UI testing, consider using launch arguments or environment variables to pass data to the application, which can then be interpreted by the app during its initialization phase.

Practical Tips

If you absolutely need to share code between your application and UI tests, you can include the necessary source files in both the application and UI test targets. However, be cautious with this approach:

  • Ensure you’re not using the shared code to modify the state of the application from within UI tests.
  • Understand that the code is running in the context of the UI test target and does not represent the actual state of the running application.

In some cases, developers have resolved similar issues by ensuring that any required packages or frameworks are correctly linked in the project settings under the “Frameworks, Libraries, and Embedded Content” section of the target’s General settings.


When dealing with “Undefined symbols for architecture x86_64” errors in UI tests, it’s crucial to understand the limitations and best practices of UI testing. By following the recommended approach and practical tips outlined above, you can ensure that your UI tests are robust and maintain the integrity of the simulated user experience.

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