docs(test-policy): create formal test policy document

[WilliamBerryiii]

Summary

The OSSF Best Practices Badge requires a formal, published test policy that states requirements for adding tests when new functionality is added. The repository has comprehensive testing infrastructure but no formal policy document.

Background

OSSF Passing Badge Criteria:

• test_policy (chore(deps)(deps): bump actions/upload-artifact from 2848b2cda0e5190984587ec6bb1f36730ca78d50 to 330a01c490aca151604b8cf639adc76d48f6c5d4 #38): GAP — "A test policy MUST be published that requires new tests for at least new major functionality"
• tests_documented_added (chore(deps)(deps): bump oxsecurity/megalinter from 6926c32998dc859ec289b8c4a06ef785cfbe3b26 to 3cbc5c0458fe4d76284c5e23a417a83d87b1a492 #39): PARTIAL — PR template has a checkbox but it is optional and unlinked to policy

Current State:

• docs/contributing/testing-validation.md (306 lines) is a how-to guide for running tests
• No formal policy statements about when tests are required
• No per-technology test requirements (Terraform, Rust, .NET, JavaScript)
• CONTRIBUTING.md does not link to a test policy
• PR template checkbox is not linked to policy

Acceptance Criteria

• A "Test Policy" section exists in docs/contributing/testing-validation.md (or a dedicated policy document)
• Policy states: new major functionality requires corresponding tests
• Policy states: bug fixes require regression tests
• Per-technology requirements documented (Terraform: plan-level .tftest.hcl, Rust: #[cfg(test)] modules, .NET: xUnit projects, JavaScript: vitest)
• CONTRIBUTING.md links to the test policy

Implementation Guidance

Add a "Test Policy" section at the top of docs/contributing/testing-validation.md with:

1. Policy statement: "All new major functionality requires corresponding automated tests. Bug fixes require regression tests that verify the fix."
2. Technology requirements table:

   Technology	Framework	Minimum Requirement
   Terraform	native terraform test	One .tftest.hcl per component with command = plan
   Rust	cargo test	#[cfg(test)] module covering core logic
   .NET	xUnit/NUnit	Test project covering business logic
   JavaScript	vitest	Test file with 80% coverage threshold

3. Cross-references: Update CONTRIBUTING.md to link to this section (PR template updates handled by IS007)