Cannot run XAMARIN UI TEST on xamarin.forms, error System.Exception

Troubleshooting “System.Exception” Errors in Xamarin.Forms UI Tests

Encountering a “System.Exception” error while running Xamarin.Forms UI tests can be frustrating. This article will guide you through common causes and solutions to resolve these errors.

Understanding the “System.Exception” Error

The “System.Exception” error is a broad catch-all message that indicates an unexpected issue has occurred during your UI test execution. It lacks specifics, making troubleshooting more challenging. To effectively diagnose the problem, you need to investigate the accompanying stack trace and error details.

Key Considerations

• Environment Setup: Ensure your test environment is properly configured, including the necessary Xamarin.Forms libraries and test frameworks (e.g., NUnit, XUnit).
• Test Project Structure: Verify your UI test project is correctly referencing the Xamarin.Forms project and that the UI test app is launched correctly.
• App under Test: Confirm that the app under test (the Xamarin.Forms application) is compiled and deployed successfully.
• App State: Ensure your application is in a consistent state when the UI test begins. This may involve steps like logging in or navigating to a specific screen.

Common Causes and Solutions

1. Missing or Incorrect Dependencies

Ensure your UI test project has the following dependencies installed:

• Xamarin.Forms NuGet package: The version should match the version used in your app under test.
• Xamarin.Forms.Xaml NuGet package: Required for using XAML in your UI test code.
• Xamarin.UITest NuGet package: Provides the UI testing framework for your tests.

2. Incorrect Test App Launch

If the UI test app is not launched correctly, the tests will fail. Verify that the correct app bundle (Android APK or iOS IPA) is being used and that the launch process is configured in the test code.

// Example UI test setup using Xamarin.UITest
[SetUp]
public void Setup()
{
    app = ConfigureApp.Android.StartApp(Xamarin.UITest.Configuration.AppDataMode.Shared);
}

3. UI Element Identification Issues

A common reason for UI tests failing is the inability to locate UI elements. Review the following:

• Element ID: Use descriptive and unique IDs for your UI elements. For example, use “loginButton” instead of “Button1.”
• Element Hierarchy: If you have nested layouts, use the `Descendants()` method to navigate through the hierarchy and identify the correct element. For instance, find a text field inside a `ScrollView` using:

  app.Query(c => c.Class("ScrollView")).Descendants(c => c.Class("TextField")).FirstOrDefault();
  

• Accessibility: Ensure your UI elements are accessible with appropriate accessibility identifiers. This aids in robust element finding.
• Element Visibility: Make sure the element you are searching for is visible on the screen before trying to interact with it. Use techniques like `WaitForElement(c => c.Marked(“loginButton”))`.

4. App State Inconsistencies

UI tests rely on a predictable app state. Any inconsistencies can lead to failures. Consider:

• Data Preloading: Load required data into your app before running tests (e.g., login credentials).
• UI Cleanup: Reset the app state (like logging out) between tests to avoid unintended dependencies.

5. Timeout Issues

Xamarin.UITest has default timeouts for element search and interaction. If your app takes longer to load or respond, adjust the timeout values. For instance:

// Set timeout for all element searches
app.App.SetTimeout(TimeSpan.FromSeconds(10));

6. Network Connectivity

Ensure your test device or emulator has reliable network connectivity if your application requires internet access. Simulate network conditions using tools like `app.SimulateNetworkSlowdown` or `app.SimulateNetworkDisconnection` to test your app’s resilience.

7. Platform-Specific Code

If you’re using platform-specific features (e.g., Android-specific permissions, iOS device features), write tests specifically for each platform to account for the differences in UI or behavior.

Debugging Tips

• Log Output: Enable logging in your UI test framework to capture detailed messages. For example, using `Console.WriteLine` or a test logging framework.
• Screen Captures: Capture screenshots at specific points during your test to visualize where the failure occurs.
• Step-by-Step Execution: Run tests in debugging mode and step through the code line by line to understand where the exception arises.
• Inspect UI Hierarchy: Tools like Xamarin.Forms Inspector or other UI inspection tools allow you to examine the UI element hierarchy and identify potential problems with element selection or visibility.

Example: Using Xamarin.UITest

Here’s a simple example illustrating UI test setup and interaction using Xamarin.UITest:

using Xamarin.UITest;

[TestFixture]
public class LoginTests
{
    private IApp app;

    [SetUp]
    public void Setup()
    {
        app = ConfigureApp.Android.StartApp(Xamarin.UITest.Configuration.AppDataMode.Shared);
    }

    [Test]
    public void Login_WithValidCredentials_Success()
    {
        app.WaitForElement(c => c.Marked("usernameEntry"));
        app.EnterText(c => c.Marked("usernameEntry"), "user");

        app.WaitForElement(c => c.Marked("passwordEntry"));
        app.EnterText(c => c.Marked("passwordEntry"), "password");

        app.Tap(c => c.Marked("loginButton"));

        app.WaitForElement(c => c.Marked("welcomeText"));
        
        // Assert that the welcome text is displayed 
        Assert.IsTrue(app.Query(c => c.Marked("welcomeText")).Any());
    }
}

Remember to adapt these examples to your specific app’s UI elements and testing needs.

Summary

Resolving “System.Exception” errors in Xamarin.Forms UI tests requires a systematic approach. By examining the error details, considering common causes, and employing effective debugging techniques, you can pinpoint the root cause and implement solutions to ensure reliable test execution. Happy testing!