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Banner showing example of backfilling unit tests for existing code with Tusk

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Overview

This guide explains how to use Tusk to generate unit and API tests for existing code through the backfill process. Tusk generates backfills at the PR/MR level. There are two types of backfill testing supported by Tusk:
  1. Unit Test Backfill: For utility functions, classes, and other standard code components
  2. API Test Backfill: For functions that make API calls
Symbol Limit: Tusk currently supports backfilling tests for a maximum of 10 symbols per PR/MR.

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Unit Test Backfill

The unit test backfill is used for standard code components such as utility functions, classes, and helper methods.

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How to Request a Regular Function Backfill

1

Add comment in code

In your IDE, add a comment inside each function/method you want to test. The comment can be single-line or multi-line.
Make sure the comment is inside the function definition and includes the keyword UseTusk.
Example:
function calculateTotal(items) {
  // [UseTusk]
  // Optional: additional context to help guide test generation
  let sum = 0;
  for (const item of items) {
    sum += item.price;
  }
  return sum;
}
2

Create a PR/MR

Raise a PR/MR that modifies the target functions/classes you want to test.
3

Wait for test generation

Tusk will detect the modified symbols and auto-generate appropriate unit tests.

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API Test Backfill

API test backfill is used when you need to generate tests for API endpoints. This requires more specific configuration to ensure proper test generation.

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Prerequisites

  • You must have a testing environment set up for API tests before using API backfill
  • If you don’t have an API testing environment configured, please contact us for assistance

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How to Request an API Test Backfill

1

Add special comment

In your IDE, add a special comment inside the function that calls the API (can be single-line or multi-line).
Make sure the comment is inside the function definition and includes the keyword UseTusk.
Example:
async function getUserData(userId) {
  /*
   * [UseTusk API]
   * source file: src/api/userService.js
   * test file: tests/api/userService.test.js
   * Please mock network responses and test error handling for 404 cases
   */
  const response = await callNewApi(`/users/${userId}`);
  return response.data;
}
2

Create a PR/MR

Create a PR/MR with the special comment that modifies the target API(s).
3

Wait for test generation

Tusk will detect the modified symbols and auto-generate appropriate API tests.

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Information in Comments

  • The comment MUST contain UseTusk for unit test generation and UseTusk API for API test generation
  • Source File (Recommended for API testing)
    • Indicate where the API implementation is located
    • Example: source file: src/api/userService.js
    • This helps Tusk trace to the API code and traverse the codebase for better test generation
  • Test File (Recommended for API testing)
    • Specify where the generated test should be saved
    • Example: test file: tests/api/userService.test.js
  • Additional Guidance (Optional)
    • You can include free-text guidance to help Tusk generate better tests. For example:
      • Specify edge cases to test
      • Provide context on the best way to write tests
    • You can reference additional context files to help guide test generation
      • Example: check src/hooks/__tests__/useAuth.test.js for inspiration on how to mock authentication
    • For more comprehensive customization options, refer to our Customization documentation where you can find information on providing global context for how to best write tests for your codebase.

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Note on Comments and File Paths

  • Tusk uses intelligent processing to extract information from your comments, so the exact format isn’t rigid
  • You can use either single-line or multi-line comment styles
  • If file paths are not provided, Tusk will attempt to determine the best locations, but we strongly recommend explicitly specifying paths to ensure tests are generated in the correct location
  • Important: All file paths (source, test, and context files) must be specified from the project root directory
  • Important: Ensure the comment is inside of the symbol definition and includes the keyword UseTusk or UseTusk API
    • Correct placement (inside the function) 
      function calculateDiscount(price, code) {
  // [UseTusk] generate unit tests
  // Implementation...
}
    • Incorrect placement (outside the function) 
      // [UseTusk] generate unit tests
function calculateDiscount(price, code) {
  // Implementation...
}

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Example Workflow

  1. Identify code that needs tests
  2. Add the appropriate UseTusk or UseTusk API comment inside the target functions
  3. Submit your PR
  4. Review the generated tests when Tusk completes the backfill
  5. Commit the tests Tusk generates with a click of a button (the UseTusk comments will be automatically removed when you commit)

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Best Practices

  • Be specific in your comments about what aspects of the code need testing
  • For API backfill, specify source and test file paths
  • Keep the number of symbols for backfill under the 10 symbol limit per PR