# Debug a Single Failing Test in Next.js with Atlas in 2026 > Atlas empowers Next.js developers to efficiently debug a single failing test by leveraging Vitest with React Testing Library and its deep understanding of the Next.js toolchain. Atlas helps Next.js developers in 2026 debug a single failing test by integrating directly with the Next.js toolchain, including `Vitest with React Testing Library` for testing, `pnpm` for package management, and `prettier` for formatting. It leverages its `bash` tool to run isolated tests, `lsp` to trace code execution, and `edit` to apply precise fixes to the production code, not the assertion. ## Key takeaways - Atlas debugs Next.js tests by directly interacting with `Vitest with React Testing Library` via `pnpm` commands. - Atlas uses its `lsp` tool to deeply understand Next.js component hierarchies and API route logic. - Every code change Atlas proposes for your Next.js project is presented as a unified diff for explicit developer approval. - Atlas leverages `bash` to run Next.js tests with specific filters and verbose flags, mirroring manual debugging techniques. - Atlas understands Next.js file paths like `app/` directory routes and `next.config.js` for accurate context. ## How does Atlas debug a single failing Next.js test? In 2026, Atlas streamlines debugging a single failing Next.js test by integrating directly with `Vitest with React Testing Library`. It leverages `bash` to isolate the test and `lsp` to work through the call graph, providing a precise approach to identifying the root cause. Atlas approaches debugging a single failing Next.js test by first isolating the problem. It uses its `bash` tool to execute the specific test with `pnpm vitest --testNamePattern "MyFailingTest"`, ensuring minimal output for focused analysis. Once the failing assertion is identified, Atlas employs its `read` tool to examine the test file and the Next.js module it exercises, such as a component in `app/components/ui/button.tsx` or an API route in `app/api/route.ts`. Atlas then utilizes its `lsp` tool to perform `goToDefinition` and `findReferences` operations, meticulously walking the call graph from the test through the Next.js application code. This deep understanding of the code's structure, built by indexing AST declarations using tree-sitter, allows Atlas to form a precise hypothesis about the failure. It can then suggest adding temporary logging statements using its `edit` tool or re-running the test with verbose flags via `bash` to confirm the hypothesis, all within the familiar Next.js development environment. ## What Next.js commands and files does Atlas use for debugging? Atlas interacts with your Next.js project using actual commands like `pnpm vitest` and navigates real file paths such as `app/dashboard/page.tsx`. This ensures that its debugging process in 2026 is concrete and directly applicable to your Next.js codebase. To debug a single failing test in a Next.js project, Atlas directly invokes the `Vitest with React Testing Library` test runner using `pnpm`. For instance, to isolate a test, Atlas executes `pnpm vitest --testNamePattern "MySpecificTest"` through its `bash` tool. This command targets only the relevant test, providing focused output. When analyzing the codebase, Atlas understands and navigates typical Next.js file structures. It can read and trace logic within `app/dashboard/page.tsx` for a page component, `app/api/users/route.ts` for an API route handler, or `components/shared/header.tsx` for a reusable UI component. Atlas also recognizes the `next.config.js` file to understand project-wide configurations and server/client boundaries, which is crucial for debugging issues specific to Next.js server components or client-side interactions. The `lsp` tool allows Atlas to jump between definitions in these files, providing a comprehensive view of the code flow that leads to the test failure. ## How does Atlas ensure safe code changes in a Next.js project? Atlas prioritizes safety in 2026 by implementing several mechanisms to protect your Next.js codebase. Every tool call is permission-gated, and all proposed code changes are presented as unified diffs for developer approval before being written to disk. Ensuring the integrity of your Next.js project is a core principle for Atlas. Before any action is taken, Atlas drafts a plan in a read-only plan agent, which you review and approve. Every Atlas tool call, whether it's `edit` to modify a Next.js component or `bash` to run a command, is permission-gated against allow, ask, and deny rules, giving you granular control. When Atlas proposes a fix to your Next.js code, for example, in `app/lib/data.ts`, it computes a unified diff for every file edit. This diff is surfaced for your approval, allowing you to meticulously review the exact changes before they are applied. For more extensive modifications spanning several hunks, Atlas can use `apply_patch`, which also generates a comprehensive diff for review. Furthermore, Atlas integrates with Git, reading branches, status, and diffs. It can stage and create commits on your behalf, and it snapshots file changes as Git patches, enabling easy diffing and rolling back of edits if needed. This multi-layered approach ensures that you, the Next.js developer, maintain full oversight and control over all code modifications. ## Steps 1. Instruct Atlas to debug a specific failing test in your Next.js project, for example: "Atlas, debug the failing test 'should display user data' in app/dashboard/__tests__/page.test.tsx." 2. Atlas uses its `bash` tool to run the isolated test with `pnpm vitest --testNamePattern "should display user data"` and analyzes the output. 3. Atlas employs its `read` tool to examine the test file (`app/dashboard/__tests__/page.test.tsx`) and the Next.js module it exercises (e.g., `app/dashboard/page.tsx` or `app/lib/fetch-data.ts`). 4. Atlas leverages its `lsp` tool to perform `goToDefinition` and `findReferences` operations, tracing the call graph through your Next.js components, server actions, or API routes. 5. Atlas forms a hypothesis and suggests adding temporary `console.log` statements to a relevant Next.js file (e.g., `app/lib/utils.ts`) using its `edit` tool, presenting a unified diff for your approval. 6. Atlas re-runs the isolated test via `bash` to verify the hypothesis with the added logging, providing the output for your review. 7. Atlas proposes a fix to the production Next.js code (e.g., `app/components/MyComponent.tsx`) using `edit` or `apply_patch`, generating a unified diff for your final approval. 8. After applying the fix, Atlas re-runs the single test, then the full `pnpm vitest` suite, and removes any temporary logging you added, ensuring a clean Next.js codebase. ## FAQ ### Can Atlas debug Next.js server components and API routes? Yes, Atlas is designed to pair with Next.js across the App Router, server components, and API routes. It understands server/client boundaries and can trace code execution within these contexts using its `lsp` tool. ### How does Atlas know my Next.js project structure and configurations? Atlas builds its code index by AST declarations using tree-sitter and reads your `next.config.js` file. It also understands the `app` directory structure, routes, and server/client boundaries, providing a comprehensive view of your Next.js project. ### What test runner does Atlas use for Next.js projects? Atlas uses `Vitest with React Testing Library` as the test runner for Next.js projects. It executes tests via `pnpm vitest` commands through its `bash` tool, allowing for precise test isolation and debugging. ### Can Atlas fix a failing assertion in a Next.js test? No, Atlas's job is to find why one specific test fails and fix the production code that the test exercises, not to modify or fix the test assertion itself. The focus is on improving the Next.js application's logic. ### How does Atlas handle `pnpm` workspaces in Next.js projects? Atlas uses `pnpm` directly for all package management operations, including running tests. It respects `pnpm`'s workspace configuration, ensuring that commands are executed correctly within your Next.js monorepo or multi-package setup. ### Is Atlas compatible with the Next.js App Router? Yes, Atlas is fully compatible with the Next.js App Router. It understands the new routing conventions, server components, and data fetching patterns introduced with the App Router, allowing it to navigate and debug code effectively. ### How does Atlas ensure my Next.js code changes are safe and reviewed? Atlas ensures safety through several layers: a read-only plan agent for initial review, permission-gated tool calls, and presenting all proposed code edits as unified diffs for your explicit approval. It also integrates with Git for easy rollback and version control. --- Canonical HTML: https://runatlas.sh/resources/stacks/debug-a-failing-test-in-nextjs Source of truth: aeo_pages row `/resources/stacks/debug-a-failing-test-in-nextjs` (segment: Stacks) (this file is generated from it, never hand-edited). Licence: Atlas is proprietary with a free core. It is not open source and there is no public source repository.