Solving the Can't seed data in mocked InMemory db in Integration tests Problem in ASP.NET Core

Learn effective strategies to seed data into an InMemory database during integration testing in ASP.NET Core applications. Follow our step-by-step guide for best practices and improved test reliability.
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Tackling the InMemory Database Seeding Issue in ASP.NET Core Integration Tests

Integration testing is a crucial part of the software development lifecycle. It helps ensure that the various components of your application work together as expected. One common issue developers encounter is the inability to seed data into a mocked InMemory database during these tests. This guide aims to guide you through troubleshooting this issue and implementing a more robust solution.

The Problem

In the context of ASP.NET Core applications, you may find instances where you have set up an integration test class to call an API endpoint, only to discover that the mocked InMemory database does not contain the expected data when you run your tests. This situation can lead to unexpected results and hinder the reliability of your tests.

Example Code

In your integration test, you likely set up your InMemory database using something like this:

[[See Video to Reveal this Text or Code Snippet]]

And you may have an API endpoint that retrieves the count of cities. Despite calling your endpoint and expecting a specific return value, you might find that the actual output does not match as shown below:

[[See Video to Reveal this Text or Code Snippet]]

Understanding the Cause

The root of the issue can mostly be traced back to how you configure your InMemory database in the test setup. When you create a new Guid for the database name during each test run, a new independent database instance is created, which means your seeded data does not persist across tests, even within the same test run.

Key Issues to Address

Database Name Generation: Using Guid.NewGuid().ToString() inside the configuration means each test gets its own separate InMemory database and any data seeded remains isolated.

Scope of the Service Provider: Creating a new service provider scope inside your Setup method can lead to unintended consequences and make your tests unpredictable.

The Solution

Step-by-Step Guide to Correct Seeding Strategy

To fix the problems discussed, follow these steps:

Freeze the Database Name: Move the Guid.NewGuid().ToString() out of the ConfigureTestServices and WithWebHostBuilder to ensure a consistent naming for the InMemory database across tests.

Modify the Setup Method: Adjust the setup method to correctly configure the database context without creating separate service providers. Here’s the revised setup method:

[[See Video to Reveal this Text or Code Snippet]]

Initial Data Seeding: Seed the database in the same scope as its context to ensure the data is present when your tests execute.

Conclusion

By making these adjustments, your integration tests should now properly seed data in the InMemory database, allowing for more reliable test results. Consistency is key in testing environments, and following these practices will lead to better outcomes while building and testing your ASP.NET Core applications.

Happy coding, and may your integration testing be bug-free!

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