Environment Interfaces in Business Central

This project contains the code used in the articles on my blog about the same topic.

The theme for this series is Super fast tests covering 100% of your code.

This 2025 series of articles is a continuation of the 2024 series called the Clean Code Initiative.

Clean Code is a prerequisite for writing good tests, but it does not guarantee code coverage by tests.

Introduction

I will introduce three different contexts of Environment Interfaces, discussed in parts 1, 2, and 3.

1. Interface against the system environment (Sandbox or Production)
2. Interface against an external API
3. Interface against the standard application

Environment interfaces usually have a single implementation within the application but can have several implementations in the test application. There is no corresponding Enum implementing the Interface.

Scenario

The app we are building communicates with an external API.

We face several key requirements:

• The app can only be in production mode when running in a production environment. If running in a sandbox, it must operate in test mode.
• Our tests must cover all code paths, including those only reachable in production mode.
• Our tests cannot call the actual API, but we still need to verify both the requests we send and how we decode the API responses.
• Tests must be extremely fast, with runtimes measured in milliseconds.
• Writing tests should be quick and cost-effective.
• We want to test only our own code, assuming that dependencies and external systems work as expected. We assume everyone else knows what they are doing

Environment Interfaces are the solution to this apparent paradox.