How to Override appsettings.json Values in ASP.NET Core Integration Tests

Learn how to easily override the connection string in your ASP.NET Core integration tests when starting the test host, ensuring seamless interactions with SQL Server containers.
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The Problem

You're in the middle of writing integration tests for your ASP.NET Core application that need to connect to a SQL Server instance running in a Docker container. To manage these connections effectively:

However, you are facing a challenge: you want to override the TestDb connection string at runtime, particularly because your tests involve starting a SQL Server container on a specific port.

Example Configuration

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

The objective is to modify the TestDb connection string right before the test host runs, to reflect the specific port where the SQL Server container is running.

The Solution

To achieve this, ASP.NET Core offers flexible configuration options that allow you to add or modify settings at runtime. Here’s a step-by-step guide on how to override the connection string using the in-memory collection.

Step 1: Configure the Test Host

When setting up your test web host using the WebHostBuilder or HostBuilder, you can customize the configuration as follows:

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

Step 2: Use the Customized Configuration

In the code snippet above, replace "your_modified_connection_string_here" with the actual connection string formatted to include the specific port for your SQL Server instance. This setup will ensure that, during test execution, your application will connect to the right database instance.

Additional Considerations

User Secrets: If applicable, you can also integrate user secrets or environment variables in your configurations for enhanced security and flexibility.

Maintainability: It’s a good practice to document these changes within your test code to ensure future maintainers understand the context of configuration overrides.

Conclusion

Take time to implement this approach in your test suite, and watch as your integration tests run seamlessly across different SQL Server instances!