docs: add test guidelines

test/Guidelines.md

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+# Base Registries Unit Testing Guidelines
+
+## Introduction
+This document outlines the guidelines for writing unit tests in C# following the "Given-When-Then" principle and encourages the use of the builder pattern for test data creation.
+
+## Given-When-Then Principle
+We adhere to the "Given-When-Then" principle to structure our unit tests. The test method naming follows the format:
+- **Given**: Describes the initial conditions.
+- **When**: Describes the action or scenario.
+- **Then**: Describes the expected outcome.
+
+### Folder Structure
+- Tests related to "When" should be organized within folders that represent the action or scenario, e.g., "WhenProposingStreetName."
+
+### Class Structure
+- Each test class should correspond to the "Given" part, e.g., "GivenMunicipality."
+
+### Method Naming
+- Test method names should follow the format: "With{Condition}_Then{Outcome}," where:
+  - "With" represents the condition being set up.
+  - "Then" represents the expected outcome of the test.
+
+## Builder Pattern for Test Data
+We encourage the use of the builder pattern to create test data. This approach provides a cleaner and more flexible way to set up test scenarios.
+
+### Test Data Builders
+- Create separate test data builder classes or methods for each class under test.
+- Builders should have clear and expressive methods for configuring the object's state.
+- Default values being set by the builder should be documented in a summary