test: Add unit tests & introduce dependency injection

[rm-hull]

Refactor the core application logic to utilize interfaces for Git and UI operations, allowing dependencies to be injected.

This enables comprehensive unit testing of the application flow and state transitions, addressing the lack of existing tests.

• Introduces app.Git and app.UI interfaces.
• Adds github.com/stretchr/testify for assertion helpers.
• Includes unit tests for app, config, and llm_provider.

[gemini-code-assist]

Summary of Changes

Hello @rm-hull, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces a significant architectural improvement by implementing dependency injection within the core application. By abstracting external dependencies like Git operations and UI interactions behind interfaces, the application becomes much easier to test and maintain. This refactoring lays the groundwork for robust unit testing, addressing a critical area for improving code quality and preventing regressions.

Highlights

• Dependency Injection: The core application logic has been refactored to use dependency injection, utilizing interfaces for Git and UI operations. This significantly improves the modularity and testability of the application.
• New Interfaces: Introduced app.Git and app.UI interfaces to abstract away concrete implementations of Git commands and user interface interactions, respectively.
• Unit Testing Framework: The github.com/stretchr/testify assertion library has been added to the project, providing a robust set of tools for writing clear and concise unit tests.
• Comprehensive Unit Tests: New unit tests have been added for the app, config, and llm_provider packages, covering various scenarios and ensuring the reliability of the refactored components.
• TODO List Update: The TODO.md file has been updated to reflect that the tasks related to adding unit tests for the core application logic and using a testing framework have been completed.

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[github-actions]

	Tests	Passed ✅	Skipped	Failed
JUnit Test Report	16 ran	16 passed	0 skipped	0 failed

Test	Result
JUnit Test Report
com/rm-hull/git-commit-summary/internal/app.TestNewApp	✅ passed
com/rm-hull/git-commit-summary/internal/app.TestAppRun/DiffError	✅ passed
com/rm-hull/git-commit-summary/internal/app.TestAppRun/NoStagedChanges	✅ passed
com/rm-hull/git-commit-summary/internal/app.TestAppRun/LLMCallError	✅ passed
com/rm-hull/git-commit-summary/internal/app.TestAppRun/TextAreaError	✅ passed
com/rm-hull/git-commit-summary/internal/app.TestAppRun/UserAborted	✅ passed
com/rm-hull/git-commit-summary/internal/app.TestAppRun/CommitError	✅ passed
com/rm-hull/git-commit-summary/internal/app.TestAppRun/Success	✅ passed
com/rm-hull/git-commit-summary/internal/app.TestAppRun	✅ passed
com/rm-hull/git-commit-summary/internal/config.TestLoad/Defaults	✅ passed
com/rm-hull/git-commit-summary/internal/config.TestLoad/WithEnvironmentVariables	✅ passed
com/rm-hull/git-commit-summary/internal/config.TestLoad	✅ passed
com/rm-hull/git-commit-summary/internal/llm_provider.TestNewProvider/GoogleProvider	✅ passed
com/rm-hull/git-commit-summary/internal/llm_provider.TestNewProvider/OpenAIProvider	✅ passed
com/rm-hull/git-commit-summary/internal/llm_provider.TestNewProvider/UnknownProvider	✅ passed
com/rm-hull/git-commit-summary/internal/llm_provider.TestNewProvider	✅ passed

• View JUnit Test Report

[coveralls]

Pull Request Test Coverage Report for Build 18959370866

Details

• 16 of 52 (30.77%) changed or added relevant lines in 7 files are covered.
• 11 unchanged lines in 2 files lost coverage.
• Overall coverage increased (+32.0%) to 32.047%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
internal/git/commit.go	0	1	0.0%
internal/git/diff.go	0	1	0.0%
internal/ui/text_area.go	0	1	0.0%
main.go	0	5	0.0%
internal/git/client.go	0	9	0.0%
internal/ui/client.go	0	19	0.0%

Files with Coverage Reduction	New Missed Lines	%
main.go	1	0.0%
internal/app/app.go	10	75.0%

Totals
Change from base Build 18958829788:	32.0%
Covered Lines:	108
Relevant Lines:	337

---

💛 - Coveralls

[gemini-code-assist]

Code Review

This pull request is an excellent refactoring effort to introduce dependency injection, which greatly improves the testability of the application. The introduction of Git and UI interfaces is well-executed, and the new unit tests for app, config, and llm_provider are comprehensive and valuable. The changes are clean and follow the stated goal of the PR. I have a couple of suggestions to further improve the separation of concerns by moving all UI logic out of the core application and into the UI layer.

[gemini-code-assist]

Printing the 'ABORTED!' message is a UI concern that should be handled by the ui component. To maintain a clean separation of concerns, consider adding a method to the UI interface for displaying this message (e.g., ShowAbortMessage()) and call it here. This would remove the direct dependency on the color package from the app package for this message.