How does Atlas handle Kotlin project setup with Gradle?

Atlas integrates direct with Kotlin projects managed by `Gradle`. When you run Atlas in a project containing a `build.gradle.kts` file, it automatically reads your modules, coroutines, and Gradle configuration. This allows Atlas to understand your project structure and execute `Gradle` commands like `gradle test` effectively.

Can Atlas generate `JUnit 5` tests for Kotlin?

Yes, Atlas can generate `JUnit 5` tests for Kotlin. Using its `write` tool, you can instruct Atlas to create new `.kt` test files within your `src/test/kotlin` directory, complete with `JUnit 5` annotations and assertions tailored to the bug you're trying to reproduce.

How does Atlas ensure my Kotlin code changes are safe?

Atlas employs several safety mechanisms for Kotlin code changes. It drafts a plan in a read-only agent, asks for permission before executing tools, and computes a unified diff for every file edit, including `.kt` files and `build.gradle.kts`, for your explicit approval before writing. This ensures you maintain full control.

Does Atlas support Kotlin coroutines?

Yes, Atlas is designed to pair with Kotlin across coroutine-based code. It can read and understand your coroutine implementations, and you can even ask Atlas to convert callbacks to coroutines or add tests for asynchronous logic, reviewing the diff before applying.

How does Atlas integrate with `ktlint` for Kotlin formatting?

Atlas is aware of the `ktlint` formatter and can be instructed to run it. This means that any new or modified Kotlin code (`.kt` files) generated or edited by Atlas can be automatically formatted to adhere to your project's `ktlint` rules, ensuring consistent code style across your codebase.

What if Atlas proposes an incorrect fix for my Kotlin bug?

If Atlas proposes an incorrect fix for your Kotlin bug, you can simply reject the proposed unified diff. Atlas's workflow is designed for developer oversight; you review and approve every change before it's written to your `.kt` files. You can then refine your instructions to Atlas or manually adjust the code.

Can Atlas help me reproduce a Kotlin bug before fixing it?

Absolutely. Atlas's `bash` tool is specifically used to reproduce bugs. You can run any `Gradle` command, such as `gradle run` or `gradle test`, to trigger the bug. Atlas captures the output and exit code, providing concrete evidence of the bug's presence before you proceed with writing a regression test or applying a fix.

How does Atlas handle `build.gradle.kts` changes?

Atlas treats `build.gradle.kts` files like any other source file. If a bug fix or a new test requires a dependency update or a change in the Gradle configuration, Atlas can propose edits to `build.gradle.kts` using its `edit` tool. These changes will also be presented as a unified diff for your review and approval.

Add a Regression Test for a Kotlin Bug Fix with Atlas in 2026

In 2026, Kotlin developers use Atlas to efficiently lock in bug fixes by first writing a regression test that fails, then applying the fix, and finally confirming the test passes using `JUnit 5 via gradle test`. This red-first, green-second approach ensures the bug is truly resolved and prevents future regressions within your Gradle-managed Kotlin project.

How Atlas helps write Kotlin regression tests?

Atlas streamlines the creation of new regression tests for Kotlin applications by leveraging its `write` tool to generate `JUnit 5` test classes. In 2026, developers specify the desired failing behavior, and Atlas drafts the `.kt` test file, often within the `src/test/kotlin` directory, ready for immediate execution.

Atlas, as a terminal-native AI coding agent, assists Kotlin developers in 2026 by generating precise regression tests. When a bug is identified, the first step is to establish a failing test case. Using the `write` tool, a developer can instruct Atlas to create a new Kotlin test file, for example, `src/test/kotlin/com/example/MyBugFixTest.kt`. Atlas understands the structure of Kotlin projects, including common testing frameworks like `JUnit 5`, and will scaffold the necessary class and test method annotations. The developer provides a clear description of the bug and the expected incorrect behavior, allowing Atlas to draft an assertion that will fail when the bug is present. This ensures the test accurately captures the bug's manifestation, adhering to the "red-first" principle of regression testing. Atlas's ability to index code by AST declarations using tree-sitter helps it understand the context of existing Kotlin code, ensuring the generated test integrates direct with the project's existing test suite and package structure.

How to run Kotlin tests with Gradle and Atlas?

Running Kotlin tests with `JUnit 5 via gradle test` is a core part of the regression workflow, and Atlas integrates this process directly using its `bash` tool. This allows developers in 2026 to execute specific tests or the entire suite, capturing the exact exit code to confirm test failures or successes.

After Atlas drafts a new Kotlin regression test, the next critical step is to prove it fails. Atlas uses its `bash` tool to execute the `JUnit 5` tests through the `Gradle` build system. A typical command would be `gradle test --tests "com.example.MyBugFixTest"`. Atlas captures the standard output and, crucially, the process exit code. A non-zero exit code unambiguously signals a test failure, confirming that the newly written test correctly reproduces the bug. This direct integration with `Gradle` means Kotlin developers don't need to leave their terminal environment or manually switch contexts. Atlas's ability to read `git` branches and status also helps ensure that the test is run against the correct codebase state, preventing false positives or negatives during the red-first phase. The `bash` tool's metadata capture is fundamental to the "red-first, green-second" discipline, providing concrete evidence of the bug's presence.

Applying bug fixes in Kotlin with Atlas's edit tool

Atlas applies bug fixes to Kotlin source files using its `edit` tool, which leverages a replacer cascade to ensure precise modifications. In 2026, developers approve a unified diff before any changes are written, providing a critical safety net for modifications to `.kt` files and `build.gradle.kts`.

Once the failing regression test is confirmed, Atlas proceeds to apply the bug fix. The `edit` tool is central to this process. A Kotlin developer instructs Atlas on the desired change, often by describing the logical correction needed. Atlas then proposes a code modification, targeting specific `.kt` files. The `edit` tool's replacer cascade requires an exact-enough `oldString` to prevent ambiguous multi-match replacements, ensuring that only the intended code block is altered. Before any changes are committed, Atlas computes a unified diff for every file edit and surfaces it for approval. This crucial step allows the Kotlin developer to review the proposed changes to their `.kt` files, `build.gradle.kts`, or any other configuration, ensuring accuracy and preventing unintended side effects. This approval mechanism, combined with Atlas's ability to snapshot file changes as `git` patches, provides robust rollback capabilities and transparency throughout the bug-fixing process.

Ensuring Kotlin code quality with Atlas and ktlint

Maintaining consistent code style in Kotlin projects is vital, and Atlas integrates with `ktlint` to ensure all generated or modified code adheres to project standards. In 2026, Atlas can automatically apply formatting rules, preventing style regressions and ensuring a clean, readable codebase after a bug fix.

Beyond fixing the bug, Atlas also helps maintain the overall quality and consistency of the Kotlin codebase. The `ktlint` formatter is a standard tool in many Kotlin projects, enforcing coding style and best practices. Atlas is aware of the project's configured `ktlint` rules and can be instructed to run `ktlint` as part of the post-fix verification or even during the `write` and `edit` phases. This ensures that any new test code or bug fix applied to `.kt` files automatically conforms to the established style guidelines. By integrating with `ktlint`, Atlas prevents the introduction of formatting inconsistencies, which can often lead to merge conflicts or reduce code readability. This attention to detail reinforces Atlas's role as a comprehensive coding agent, not just a bug fixer, but a guardian of code quality in 2026 Kotlin development.

Atlas's safety and review for Kotlin changes

Atlas prioritizes safety and developer control for all Kotlin code modifications, employing a read-only plan agent and permission-gated tool calls. In 2026, every proposed change to `.kt` files or `build.gradle.kts` is presented as a unified diff for explicit approval, ensuring transparency and preventing unintended alterations.

Atlas is designed with multiple layers of safety and review, crucial for any changes to a production Kotlin codebase. Before executing any modifications, Atlas drafts a plan in a read-only plan agent, allowing the developer to understand the intended sequence of operations. Every Atlas tool call, including `bash`, `write`, and `edit`, is permission-gated against allow, ask, and deny rules, giving the developer granular control over what actions Atlas can take. For Kotlin-specific changes, such as modifying a `.kt` source file or adjusting `build.gradle.kts`, Atlas computes a unified diff and surfaces it for approval before writing. This explicit approval step is a non-negotiable safeguard, ensuring that the developer reviews and confirms every line change. Furthermore, Atlas reads `git` branches, status, and diffs, and can stage and create commits on your behalf, integrating direct into existing Kotlin development workflows while maintaining full transparency and auditability of all changes.

Step by step

01Reproduce the Kotlin bug with `bash`: Use Atlas's `bash` tool to run the existing application or a minimal script that reliably triggers the bug. Capture the exact command and output, noting any stack traces or error messages from your Kotlin application. For example, `atlas bash "gradle run --args='buggy_input'"`.
02Write the failing Kotlin regression test with `write`: Instruct Atlas using the `write` tool to create a new `JUnit 5` test file, such as `src/test/kotlin/com/example/MyBugFixTest.kt`. Describe the bug and the expected incorrect behavior, ensuring the test asserts on this behavior so it will fail.
03Confirm the Kotlin test fails with `bash`: Execute the newly written `JUnit 5` test using Atlas's `bash` tool and `gradle test`. For instance, `atlas bash "gradle test --tests 'com.example.MyBugFixTest'"`. Verify that the `bash` command returns a non-zero exit code, confirming the test fails as expected.
04Apply the Kotlin bug fix with `edit`: Use Atlas's `edit` tool to describe and apply the necessary code changes to your Kotlin source files (`.kt`). Atlas will propose modifications, and you will review and approve the unified diff before it writes the changes.
05Re-run the Kotlin test and confirm pass with `bash`: Execute the same `gradle test` command from step 3 using Atlas's `bash` tool. Confirm that the test now passes (exit code 0).
06Run the wider Kotlin test suite and format with `ktlint`: After confirming the specific regression test passes, use `atlas bash "gradle test"` to run the entire `JUnit 5` test suite to check for collateral damage. Optionally, run `atlas bash "ktlint --fix"` to ensure all `.kt` files adhere to formatting standards.
07Review and commit Kotlin changes with Atlas: Review the final `git` diff presented by Atlas, which includes the new test and the bug fix. Use Atlas to stage and create a commit message for your Kotlin project.

Frequently asked questions

How does Atlas handle Kotlin project setup with Gradle?: Atlas integrates direct with Kotlin projects managed by `Gradle`. When you run Atlas in a project containing a `build.gradle.kts` file, it automatically reads your modules, coroutines, and Gradle configuration. This allows Atlas to understand your project structure and execute `Gradle` commands like `gradle test` effectively.
Can Atlas generate `JUnit 5` tests for Kotlin?: Yes, Atlas can generate `JUnit 5` tests for Kotlin. Using its `write` tool, you can instruct Atlas to create new `.kt` test files within your `src/test/kotlin` directory, complete with `JUnit 5` annotations and assertions tailored to the bug you're trying to reproduce.
How does Atlas ensure my Kotlin code changes are safe?: Atlas employs several safety mechanisms for Kotlin code changes. It drafts a plan in a read-only agent, asks for permission before executing tools, and computes a unified diff for every file edit, including `.kt` files and `build.gradle.kts`, for your explicit approval before writing. This ensures you maintain full control.
Does Atlas support Kotlin coroutines?: Yes, Atlas is designed to pair with Kotlin across coroutine-based code. It can read and understand your coroutine implementations, and you can even ask Atlas to convert callbacks to coroutines or add tests for asynchronous logic, reviewing the diff before applying.
How does Atlas integrate with `ktlint` for Kotlin formatting?: Atlas is aware of the `ktlint` formatter and can be instructed to run it. This means that any new or modified Kotlin code (`.kt` files) generated or edited by Atlas can be automatically formatted to adhere to your project's `ktlint` rules, ensuring consistent code style across your codebase.
What if Atlas proposes an incorrect fix for my Kotlin bug?: If Atlas proposes an incorrect fix for your Kotlin bug, you can simply reject the proposed unified diff. Atlas's workflow is designed for developer oversight; you review and approve every change before it's written to your `.kt` files. You can then refine your instructions to Atlas or manually adjust the code.
Can Atlas help me reproduce a Kotlin bug before fixing it?: Absolutely. Atlas's `bash` tool is specifically used to reproduce bugs. You can run any `Gradle` command, such as `gradle run` or `gradle test`, to trigger the bug. Atlas captures the output and exit code, providing concrete evidence of the bug's presence before you proceed with writing a regression test or applying a fix.
How does Atlas handle `build.gradle.kts` changes?: Atlas treats `build.gradle.kts` files like any other source file. If a bug fix or a new test requires a dependency update or a change in the Gradle configuration, Atlas can propose edits to `build.gradle.kts` using its `edit` tool. These changes will also be presented as a unified diff for your review and approval.

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