Add unit testing guidelines to Contribute.md (#114)

* Initial plan

* Add comprehensive testing notes to Contribute.md

Co-authored-by: aholstrup1 <117829001+aholstrup1@users.noreply.github.com>

* Remove E2E testing documentation, keep only unit tests

Co-authored-by: aholstrup1 <117829001+aholstrup1@users.noreply.github.com>

* Update unit test best practices

Removed the guideline to follow the Arrange-Act-Assert pattern from best practices for unit tests.

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: aholstrup1 <117829001+aholstrup1@users.noreply.github.com>

Author: Copilot

Scenarios/Contribute.md

@@ -43,10 +43,79 @@ Please ensure that all unit tests run and create a Pull Request against [https:/
 
 In the AL-Go repository we use a number of precommit hooks to help us identify issues in the code. We run the precommit hooks locally but also as a PR check. In order to ensure this check passes please install pre-commit in your local AL-Go repository. Pre-Commit can be installed by following the instructions on https://pre-commit.com/#quick-start. Once the precommint hooks are installed you can run `pre-commit run --all-files` to verify your changes.
 
+## Testing your contributions
+
+When contributing to AL-Go, it's important to add tests for your changes to ensure code quality and prevent regressions.
+
+**When to add tests:**
+
+- **Always add unit tests** for new functions, modules, or bug fixes
+- **Update existing tests** if you modify existing functionality
+- **Ensure all tests pass** before submitting a pull request
+
+Unit tests in AL-Go are fast, isolated tests that verify individual functions and modules using the Pester testing framework.
+
+The section below provides detailed guidance on how to add unit tests.
+
 ## Unit tests
 
 The Tests folder, in the AL-Go repository, contains a number of unit-tests. Open Tests/runtests.ps1 in VS Code and select Run. Unit tests are quick and will run on every PR and every Push. We will be adding a lot of unit tests going forward.
 
+### How to add unit tests
+
+When contributing to AL-Go, you should add unit tests for your changes. Unit tests in AL-Go use the [Pester](https://pester.dev/) testing framework for PowerShell.
+
+**Creating a new unit test file:**
+
+1. Create a new `.Test.ps1` file in the `Tests` folder. The file name should describe what you're testing (e.g., `MyFeature.Test.ps1`)
+2. Import the module or script you want to test at the beginning of your test file
+3. Use `Describe` blocks to group related tests
+4. Use `It` blocks for individual test cases
+5. Use `BeforeAll` for setup that runs once before all tests in a `Describe` block
+6. Use `Mock` to mock external dependencies and function calls
+
+**Example test structure:**
+
+```powershell
+Import-Module (Join-Path $PSScriptRoot '../Actions/.Modules/MyModule.psm1') -Force
+
+Describe "MyFeature tests" {
+    BeforeAll {
+        # Setup code that runs once
+    }
+
+    It 'Should do something specific' {
+        # Arrange
+        Mock Write-Host { }
+        
+        # Act
+        $result = MyFunction -Parameter "value"
+        
+        # Assert
+        $result | Should -Be "expected"
+    }
+}
+```
+
+**Best practices for unit tests:**
+
+- Test one thing per `It` block
+- Use descriptive test names that explain what is being tested
+- Mock external dependencies to isolate the code under test
+- Clean up temporary files and folders created during tests
+- Use `InModuleScope` when you need to test private functions within a module
+
+**Running unit tests locally:**
+
+```powershell
+# Run all unit tests
+pwsh -File Tests/runtests.ps1 -Path Tests
+
+# Or run from VS Code by opening Tests/runtests.ps1 and selecting Run
+```
+
+The CI workflow automatically runs all unit tests on both Windows (PowerShell 5) and Linux (PowerShell 7) when you create a pull request.
+
 ## End to End tests
 
 In the e2eTests folder, in the AL-Go repository, there are 3 types of end to end tests.