In 2026, Atlas helps Terraform HCL developers write unit tests for untested code by leveraging the `terraform test` runner, `terraform init (module registry)` for module dependencies, and `terraform fmt` for consistent formatting, ensuring your infrastructure code is thoroughly validated and adheres to established conventions.
How Atlas identifies untested Terraform HCL code
Atlas identifies untested Terraform HCL code by first reading the target module and then using its `lsp` tool with the `documentSymbol` operation to enumerate all exported symbols, ensuring no public function is missed. This process helps pinpoint exactly which 0 modules or resources currently lack test coverage, providing a clear starting point for test development.
To begin writing unit tests for a Terraform HCL module, Atlas first needs to understand its structure and public interface. Atlas uses its `read` tool to ingest the `.tf` files within your root module, including resources, variables, outputs, and the provider versions pinned in your `.terraform.lock.hcl` file. Following this, Atlas employs its `lsp` tool, specifically the `documentSymbol` operation, to extract a comprehensive list of all exported symbols. This includes every `resource` block, `variable` definition, and `output` declaration that the module exposes. By enumerating these symbols, Atlas ensures that every public component of your Terraform HCL module is considered for testing, preventing any critical parts from being overlooked. This detailed understanding forms the foundation for generating relevant and complete test cases, aligning with the goal of adding real tests for a module that currently has none.
How Atlas learns Terraform HCL testing conventions
To ensure new tests integrate direct, Atlas learns existing Terraform HCL testing conventions by using its `grep` tool to search for an existing test file within the repository. This allows Atlas to replicate the module's framework, import style, and naming conventions, ensuring the 100% consistency expected in a professional codebase and making new tests indistinguishable from existing ones.
A crucial aspect of adding tests to an existing Terraform HCL codebase is adhering to its established conventions. Atlas achieves this by leveraging its `grep` tool. Atlas searches your repository for existing test files, typically located in a `tests/` directory, to identify how `terraform test` cases are structured. This includes observing how `variable` blocks are defined for test inputs, how `output` blocks are used for assertions, and the overall naming scheme for test files and individual `run` blocks. By analyzing these existing patterns, Atlas can generate new test specifications that perfectly match your team's preferred style, import statements, and file organization. This capability is vital for maintaining a clean, consistent, and easily maintainable test suite, ensuring that the new tests feel native to the repository rather than being an alien addition.
Writing and running Terraform HCL unit tests with Atlas
Atlas writes new Terraform HCL unit test specifications using its `write` tool, which presents a unified diff for approval before any changes are committed to disk. Once drafted, Atlas executes the test suite with the `bash` tool, invoking the native `terraform test` runner to validate the module's behavior, even if the output exceeds 2000 lines or 50 KB, with the full log saved for review.
After understanding the module's interface and existing test conventions, Atlas proceeds to write the actual Terraform HCL unit tests. Using its `write` tool, Atlas drafts the new test files, typically placing them in a `tests/` subdirectory alongside your module. Before any changes are applied, Atlas computes a unified diff for every proposed file edit and surfaces it for your approval. This permission prompt ensures you have full control over the generated code. Once approved, Atlas uses its `bash` tool to run the test suite. This involves executing the actual `terraform test` command, which is the standard test runner for Terraform HCL. Atlas monitors the output, reading failures and successes. If the output exceeds 2000 lines or 50 KB, Atlas truncates the display in the terminal but saves the full log to a file, ensuring you can always access complete diagnostic information. This direct execution of `terraform test` provides immediate feedback on the correctness of the new test cases and the module under test.
Iterating and refining Terraform HCL tests
Refining Terraform HCL tests with Atlas involves an iterative process using the `edit` tool to address failures reported by `terraform test`. For larger modules, Atlas can maintain progress with a `todowrite` list, ensuring that all 100% of identified issues are systematically resolved until the entire test suite is green and the module is thoroughly validated.
The process of writing tests is rarely a one-shot operation; it often requires iteration to achieve a passing suite. When `terraform test` reports failures, Atlas facilitates the debugging and refinement process using its `edit` tool. You can instruct Atlas to modify specific parts of the test code or even the module itself based on the test output. For complex Terraform HCL modules or extensive test suites, Atlas can help manage the remaining work by maintaining a `todowrite` list, ensuring that all identified issues are tracked and addressed systematically. After each edit, Atlas can re-run `terraform test` to verify the fixes. Once the tests pass, Atlas also ensures that the new test files adhere to formatting standards by running `terraform fmt -recursive`, maintaining code consistency. Atlas can then read git branches, status, and diffs, and can stage and create commits on your behalf, making the entire workflow from test creation to commit direct.
Ensuring safety and review for Terraform HCL changes
Atlas prioritizes safety and review for all Terraform HCL changes by implementing permission-gated tool calls and presenting a unified diff for every file edit before writing. This ensures that every proposed modification, from adding a new `resource` block to updating a `variable` definition, receives explicit approval, preventing unintended infrastructure changes 100% of the time.
Working with Terraform HCL means directly impacting infrastructure, making safety and review paramount. Atlas is designed with multiple layers of safeguards. Every Atlas tool call, including `write` and `bash`, is permission-gated against allow, ask, and deny rules, requiring your explicit consent before execution. When Atlas drafts a plan, it does so in a read-only plan agent, allowing you to review the proposed actions without any risk of unintended changes. For any file modification, Atlas computes a unified diff and surfaces it for your approval before writing anything to disk. This applies to new `terraform test` files, modifications to existing `.tf` configurations, or even the output of `terraform fmt`. Furthermore, Atlas can run `terraform validate` and `terraform plan` behind a permission prompt, allowing you to read the plan diff with Atlas before anything is applied. Atlas also snapshots file changes as git patches, so edits can be diffed and rolled back, providing an additional layer of safety and auditability for all your Terraform HCL development.
Step by step
- 01Run Atlas in your Terraform root module, ensuring `.tf` files and a `.terraform.lock.hcl` are present for Atlas to read.
- 02Ask Atlas to `read` the target Terraform HCL module and use its `lsp` tool with `documentSymbol` to enumerate all exported resources, variables, and outputs.
- 03Instruct Atlas to `grep` for existing test files in your repository's `tests/` directory to learn current `terraform test` conventions and idioms.
- 04Have Atlas `write` the new Terraform HCL unit test spec file in the `tests/` directory, carefully reviewing the proposed unified diff for approval.
- 05Approve Atlas to `bash` execute the `terraform test` command to run the newly created test suite and observe any failures.
- 06Use Atlas's `edit` tool to fix any reported `terraform test` failures and then run `terraform fmt -recursive` to ensure consistent HCL formatting.
- 07Approve Atlas to stage and create a git commit for the new, passing Terraform HCL test files and any related module changes.
Frequently asked questions
- How does Atlas ensure my Terraform HCL tests match existing patterns?
- Atlas uses its `grep` tool to scan your repository for existing `tests/` files, extracting the framework, import style, and naming conventions to apply to new Terraform HCL unit tests, ensuring direct integration.
- Can Atlas run `terraform test` directly?
- Yes, Atlas uses its `bash` tool to directly invoke the `terraform test` command, allowing you to see real-time results and failures for your Terraform HCL modules within the terminal.
- What if my Terraform HCL module has no existing tests?
- If no existing `tests/` are found, Atlas will propose a standard `terraform test` structure based on best practices, then iterate with you to refine it, ensuring your new Terraform HCL tests are robust and well-formed.
- How does Atlas handle large Terraform HCL test outputs?
- For `terraform test` outputs exceeding 2000 lines or 50 KB, Atlas truncates the display in the terminal but saves the full log to a file, ensuring you can always access complete diagnostic information for your Terraform HCL tests.
- Is it safe to let Atlas modify my Terraform HCL code?
- Yes, Atlas operates with permission-gated tool calls, drafts plans in a read-only agent, and presents a unified diff for every proposed Terraform HCL file edit, requiring your explicit approval before writing any changes.
- Does Atlas support `terraform fmt` for HCL test files?
- Absolutely. Atlas integrates `terraform fmt -recursive` to automatically format all new and modified Terraform HCL test files, maintaining code consistency and adherence to your project's style guidelines.
- How does Atlas identify what to test in a Terraform HCL module?
- Atlas uses its `lsp` tool with the `documentSymbol` operation to enumerate all exported resources, variables, and outputs from your Terraform HCL module, ensuring comprehensive test coverage for its public interface.
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