tests: prevent repo file modifications during test runs

[blindzero]

Problem Statement

During test execution (Invoke-Pester), some tests currently generate or modify files inside the repository working tree (e.g. documentation or reference artifacts).

This leads to several issues:

• git status becomes dirty after running tests
• developers are prompted to commit changes they did not intend to make
• CI and local test behavior diverges
• unit tests have side effects outside their execution scope

--> Tests must be side-effect free with regard to the repository state.

Proposed Solution

• Ensure that running tests never modifies committed files
• Clearly distinguish between:
  • fixtures (static, committed test data)
  • generated artifacts (temporary test output)
• Improve test isolation and developer experience
• Keep CI and local test runs fully deterministic

Scope / Planned Changes

1. Test Output Redirection

• All generator or writer logic invoked from tests must write to $TestDrive
• No test may write to:
  • docs/
  • references/
  • repo root
  • any committed path

2. Fixtures vs. Generated Files

• Static test inputs and expected outputs must be moved to: tests/fixtures/
• Tests read fixtures via Get-Content, Import-*, etc.
• Fixtures are committed and reviewed like normal source files

3. Generator Tests (“Golden Master” Pattern)

• Documentation / reference generators:
  • generate output into $TestDrive
  • compare generated output against committed reference files
• Tests must not regenerate committed documentation in-place

4. Optional Safety Net (if applicable)

• Generator code may support a configurable output location via:
  • -OutputPathparameter and/or
  • environment variable override (e.g. IDLE_OUTPUT_DIR)
• Tests must always set this to $TestDrive

5. Cleanup

• Ensure no temporary artifacts remain after test execution
• Invoke-Pester must leave git status clean

Out of Scope

• No functional changes to IdLE engine logic
• No changes to step behavior or provider contracts
• No documentation regeneration as part of this issue

Acceptance Criteria / Definition of Done

• Running Invoke-Pester does not modify the working tree
• git status is clean after a test run
• All generated files during tests are written to $TestDrive
• Fixtures are clearly separated under tests/fixtures
• CI (Windows + Linux) passes without repo modifications
• No test relies on implicit filesystem side effects

Notes

This issue focuses on test hygiene and developer experience only and must be implemented as a standalone PR, separate from functional or feature-related changes.

[blindzero]

in the meantime clean, all tests with "Set-Content" use "Testdrive" and dont create files in repo anymore.