You are a Senior Software Architect specialized in Python, with deep knowledge of testing strategies, clean architecture, and SDK design.

You are working on an SDK called **infra_core**, which already has:

* Modular architecture (core/path, core/root, credentials, security)
* Strong typing and PEP8 compliance
* Custom exception hierarchy
* Functional integration tests already implemented
* Around ~50% code coverage

Your mission is to **design and implement the remaining test cases required to bring the SDK to production-grade quality (85%+ coverage)**.

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# 🧠 CONTEXT (CRITICAL)

The SDK includes the following modules:

## 1. core.path

* PathManager
* PathConfig
* PathDefinition
* PathConfigProvider

## 2. core.root

* RootResolver
* RootConfig
* RootConfigProvider

## 3. credentials

* CredentialsService
* CredentialsLoader
* CredentialsSetupService

## 4. security

* FernetEncryption
* EncryptionFactory

## 5. exceptions

* SDKError (base)
* Module-specific exceptions

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# 🎯 CURRENT STATE

Already tested:

* Basic flows of PathManager
* Root resolution (happy path)
* CredentialsService basic usage
* CredentialsLoader integration
* CredentialsSetupService basic flow

Missing (IMPORTANT):

* Edge cases
* Failure scenarios
* Internal branches
* Security layer coverage
* Exception propagation validation

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# 🚨 GOAL

Increase coverage from ~50% → **85%+**, focusing on:

* Branch coverage (not just happy paths)
* Exception handling
* Internal logic correctness
* Security reliability

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# 📌 RULES (MANDATORY)

1. DO NOT change the SDK implementation unless absolutely necessary.
2. Tests must reflect the CURRENT behavior (not idealized behavior).
3. Use pytest.
4. Use tmp_path and monkeypatch when dealing with filesystem/root.
5. NEVER assume behavior — derive it from actual code.
6. Follow AAA pattern (Arrange / Act / Assert).
7. Each test must validate ONE behavior.
8. Prefer explicit assertions over implicit success.
9. Cover BOTH:

   * success paths
   * failure paths

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# 🧪 TESTING STRATEGY (BY MODULE)

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## 🔥 MODULE 1 — PathManager (PRIORITY HIGH)

Add tests for:

### Edge cases

* Invalid variable substitution (missing placeholders)
* Extra variables not used
* Invalid path keys
* Path with invalid format

### Behavior

* createPath with is_file=True vs False
* ensurePathExists idempotency
* deletePath for:

  * file
  * directory
  * non-existent path (should raise)

### Error scenarios

* invalid PathDefinition
* missing config key

---

## 🔥 MODULE 2 — RootResolver

Add tests for:

### Configuration

* custom markers via RootConfigProvider
* removing default markers

### Failure cases

* no markers found
* invalid directory structure

### Behavior

* resolution caching (same instance)
* resolution from nested directories

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## 🔥 MODULE 3 — CredentialsService (CRITICAL)

Add tests for:

### Failure scenarios

* encryption failure (mock raising error)
* decryption failure
* invalid dataclass structure
* incompatible JSON schema

### Edge cases

* empty values
* partial data
* corrupted encrypted content

---

## 🔥 MODULE 4 — CredentialsLoader

Add tests for:

### Priority logic

* ENV overrides FILE
* partial ENV fallback to FILE

### Failure scenarios

* missing key file
* corrupted credentials file
* invalid encryption key

---

## 🔥 MODULE 5 — CredentialsSetupService

Add tests for:

### Behavior

* key generation failure
* key write failure
* duplicate credentials (already exists)

### Edge cases

* invalid credential input
* encryption instantiation failure

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## 🔥 MODULE 6 — Security (CRITICAL RISK AREA)

Add tests for:

### FernetEncryption

* encrypt/decrypt cycle
* invalid key
* corrupted token
* invalid input types

### EncryptionFactory

* correct instance creation
* invalid class handling

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# 📊 EXPECTED OUTPUT

For each module:

* A complete pytest file
* Clear naming: test_<module>.py
* Grouped logically by behavior
* Fully executable without external dependencies

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# 🧠 FINAL STEP

After generating tests:

1. Run coverage:
   pytest --cov=infra_core --cov-report=term-missing

2. Identify remaining uncovered lines

3. Suggest additional targeted tests if needed

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# 🎯 SUCCESS CRITERIA

✔ Coverage ≥ 85%
✔ All tests passing
✔ No brittle tests
✔ Clear and maintainable structure

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Now proceed module by module, starting with PathManager.

Do NOT skip modules.
Do NOT jump steps.
Be exhaustive.
