docs(CONTRIBUTING): add testing guidelines and example structure

- Introduced a new section on running tests using Mocha, detailing commands for executing the test suite and specific test files.
- Provided guidelines for writing tests, including file placement, naming conventions, and best practices for structuring tests.
- Included an example test structure to illustrate the recommended approach for organizing test cases.

These additions enhance the documentation for contributors, ensuring clarity on testing practices and improving overall project maintainability.

Author: joshmu

CONTRIBUTING.md

@@ -21,6 +21,34 @@ To get started with contributing, please follow these steps:
 5. Commit your changes and push them to your forked repository.
 6. Open a pull request to the main repository.
 
+### Running Tests
+
+The project uses Mocha for testing. To run the test suite:
+
+1. Run all tests: `npm test`
+2. Run specific test file: `npm test -- path/to/test`
+
+When writing tests:
+
+- Place test files in `src/test/suite/`
+- Use the naming convention `*.test.ts`
+- Group related tests using `suite()` and `test()`
+- Keep tests focused and simple
+- Mock external dependencies
+- Use descriptive test names that explain the expected behavior
+
+Example test structure:
+
+```typescript
+suite('Feature Name', () => {
+  test('should handle specific case', async () => {
+    // Arrange
+    // Act
+    // Assert
+  });
+});
+```
+
 ### Running the extension
 
 Open the extension project in VS Code (e.g. by running `code .` in the project folder).