Atlas helps Swift developers in 2026 write unit tests for untested code by leveraging the Swift Package Manager and XCTest via `swift test`, ensuring new tests match existing repository conventions and providing a safe, reviewable workflow.
How Atlas identifies untested Swift code for XCTest generation
Atlas in 2026 streamlines the process of writing unit tests for Swift modules by first reading the target module and enumerating its exported symbols using the `lsp` tool's `documentSymbol` operation. This ensures comprehensive test coverage for all public functions.
To begin writing unit tests for a Swift module that lacks coverage, Atlas first uses its `read` tool to ingest the target module's source code. Following this, Atlas employs the `lsp` tool with its `documentSymbol` operation to precisely identify all exported symbols, such as public functions, classes, and protocols, within that Swift module. This detailed symbol enumeration is crucial for ensuring that no public API is missed when generating new `XCTest` cases. By understanding the module's structure and public interface, Atlas can then systematically draft tests that cover each identified symbol, laying the groundwork for a robust `XCTest` suite within your Swift Package Manager project.
Matching Swift testing conventions for new XCTest files
To maintain consistency, Atlas in 2026 identifies existing Swift testing conventions by using the `grep` tool to locate an existing test file within the repository. This allows Atlas to adopt the project's specific `XCTest` framework, import style, and naming conventions.
A key aspect of integrating new tests into an existing Swift codebase is adhering to established conventions. Atlas achieves this by utilizing the `grep` tool to search for an existing `XCTest` file, for example, `MyModuleTests/MyModuleTests.swift`, within your Swift Package Manager project. By analyzing the structure, import statements, and naming patterns of an existing test file, Atlas learns the repository's preferred `XCTest` framework usage. This ensures that any new test files, such as `NewModuleTests/NewModuleTests.swift`, generated by Atlas with the `write` tool, direct blend with the project's current testing style, making them immediately recognizable and maintainable by Swift developers.
Executing Swift unit tests with `swift test` and iterating with Atlas
After drafting new `XCTest` cases, Atlas in 2026 executes the Swift unit test suite using the `bash` tool with the `swift test` command. This crucial step verifies the tests' functionality, with Atlas reading failures and saving full logs for review.
The true measure of a test is its execution. Once Atlas has drafted the new `XCTest` cases for your Swift module, it immediately runs the entire test suite using the `bash` tool with the `swift test` command. This command, part of the Swift Package Manager toolchain, compiles and executes all `XCTest` cases. Atlas then captures the output, reading any failures to identify areas needing refinement. If the output exceeds 2000 lines or 50 KB, Atlas truncates it for display but saves the full log to a file for comprehensive review. The workflow then enters an iterative loop: Atlas uses the `edit` tool to make necessary adjustments to the Swift test code, repeating the `swift test` execution until all tests pass. For large Swift modules, Atlas can maintain progress using a `todowrite` list, ensuring systematic coverage.
Reviewing and approving Swift code changes with Atlas's safety features
Atlas in 2026 prioritizes safety and developer control when modifying Swift code by presenting a unified diff for every file edit before writing to disk. This permission-gated process ensures that all changes, including new `XCTest` files, are explicitly approved by the developer.
Developer control and code integrity are paramount when Atlas modifies a Swift codebase. Before any changes, such as new `XCTest` files or modifications to existing Swift source, are written to disk, Atlas computes and displays a unified diff. This diff clearly shows every proposed alteration, allowing the Swift developer to review the exact changes. Every Atlas tool call, including those from the `write` and `edit` tools, is permission-gated against allow, ask, and deny rules, requiring explicit approval before execution. This ensures that all modifications, from adding `XCTest` cases to adopting `async/await` patterns, are transparent and approved. Furthermore, Atlas snapshots file changes as `git` patches, enabling easy diffing and rollback of edits if needed, providing a robust safety net for your Swift project.
Step by step
- 01Run `atlas` in your Swift package directory, ensuring a `Package.swift` file is present.
- 02Use `atlas read` to analyze the target Swift module and `atlas lsp documentSymbol` to enumerate its public symbols for `XCTest` coverage.
- 03Employ `atlas grep` to find an existing `XCTest` file (e.g., `MyModuleTests/MyModuleTests.swift`) to learn the repository's testing conventions and `XCTest` style.
- 04Draft a new `XCTest` file (e.g., `NewModuleTests/NewModuleTests.swift`) using `atlas write`, carefully reviewing the unified diff before approving the changes.
- 05Execute the new `XCTest` suite with `atlas bash "swift test"`, observing the output for any failures reported by the Swift Package Manager.
- 06Iterate on test failures using `atlas edit` to refine the Swift test code, leveraging `todowrite` for tracking progress on large modules.
- 07Review the final, passing `XCTest` changes, then use Atlas's `git` capabilities to stage and create a commit on your behalf.
Frequently asked questions
- How does Atlas ensure new Swift tests match my project's style?
- Atlas uses the `grep` tool to analyze existing `XCTest` files, identifying and replicating your project's specific framework, import style, and naming conventions for new Swift tests.
- What Swift testing framework does Atlas use?
- Atlas works directly with `XCTest`, the standard testing framework for Swift, and executes tests using the `swift test` command via the Swift Package Manager.
- Can Atlas add tests to a Swift module that uses `async/await`?
- Yes, Atlas is capable of adding `XCTest` cases that adopt `async/await` patterns, integrating direct with modern Swift concurrency features.
- How does Atlas handle large Swift modules with many untested functions?
- For large Swift modules, Atlas can use a `todowrite` list to track progress, ensuring all public symbols identified by the `lsp` tool receive appropriate `XCTest` coverage.
- How does Atlas prevent accidental changes to my Swift codebase?
- Atlas provides a unified diff for every proposed file edit and requires explicit approval before writing any changes to disk, ensuring full control over your Swift project.
- What Swift package manager does Atlas support?
- Atlas fully supports the Swift Package Manager, allowing it to read your targets, protocols, and dependencies within a `Package.swift` file.
- Does Atlas integrate with `swift-format` for code style?
- While Atlas focuses on generating functional `XCTest` code, its plugin system allows for integration with tools like `swift-format` to ensure adherence to Swift code style guidelines.
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