Add unit tests for OpenAiProvider

[noruzzamans]

Description

This PR introduces a dedicated unit test suite for the OpenAiProvider class (WordPress\OpenAiAiProvider\Provider\OpenAiProvider).

OpenAiProvider is the central entry class for the AI Provider for OpenAI. It handles:

• Base URL and endpoint construction (url()).
• Provider metadata creation (metadata()) including ID, name, cloud type, API key authentication, localized descriptions, and SVG logo path.
• Model directory instantiation (modelMetadataDirectory()) and provider availability checking (availability()).
• Factory dispatching for all supported model capabilities:
  • Text generation (OpenAiTextGenerationModel)
  • Image generation (OpenAiImageGenerationModel)
  • Embedding generation (OpenAiEmbeddingGenerationModel)
  • Text-to-speech conversion (OpenAiTextToSpeechConversionModel)
• Exception handling for unsupported capabilities (RuntimeException).

While individual model and directory classes had unit tests, OpenAiProvider itself previously lacked dedicated test coverage.

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Test Coverage Summary

The newly added test suite (tests/unit/Provider/OpenAiProviderTest.php) contains 10 tests and 25 assertions covering:

1. Base URL & Endpoint Construction: Asserts url() resolves https://api.openai.com/v1 and correctly formats subpaths with or without leading slashes.
2. Provider Metadata Verification: Confirms all provider metadata properties (id, name, cloud type, credentials URL, authentication method, localized description, logo path).
3. Directory & Availability Instantiation: Asserts proper class instances and verifies static caching across consecutive calls.
4. Model Factory Capabilities: Tests that text, image, embedding, and text-to-speech capabilities correctly resolve to their corresponding model instances.
5. Unsupported Capabilities & Error Handling: Asserts RuntimeException is thrown with expected error messages for unknown or empty capability sets.

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Verification & Testing

All local test suites and linters pass cleanly:

# Isolated unit tests
vendor/bin/phpunit tests/unit/Provider/OpenAiProviderTest.php

# Full unit test suite (60 tests, 243 assertions)
vendor/bin/phpunit

# Coding standards (PER / PSR-12)
composer phpcs

# Static analysis (Level MAX)
composer phpstan

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Use of AI Tools

AI assistance: Yes
Model(s): Gemini 3.8 Flash High
Used for: Authoring PHPUnit unit tests for OpenAiProvider and drafting PR documentation. Code was manually reviewed, locally executed, and verified.

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Co-authored-by: noruzzamans <noruzzaman@git.wordpress.org>
Co-authored-by: saarnilauri <laurisaarni@git.wordpress.org>

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[saarnilauri]

Solid looking PR with a nice test addition for a class that genuinely had no direct coverage.

I added few comments that might be good additions to the PR.

[noruzzamans]

Solid looking PR with a nice test addition for a class that genuinely had no direct coverage.

I added few comments that might be good additions to the PR.

Thank you @saarnilauri for the helpful review and guidance!

I have accepted all 3 suggestions and updated the tests to cover the capability-skipping and precedence paths you mentioned. All tests and linters pass cleanly.

Could you please take another look when you get a chance?

[saarnilauri]

Thanks. The first round changes landed well. See the comments for few more followup changes I suggest.

[saarnilauri]

Thank you again. Now approving.