Jest: Conditional Test Path Exclusion

This challenge focuses on a common requirement in software development: selectively ignoring certain test paths during execution. This is useful for managing test suites that might be environment-specific, under active development, or for temporarily disabling flaky tests. You will learn how to leverage Jest's capabilities to conditionally skip tests based on specific criteria.

Problem Description

You are tasked with creating a mechanism in Jest to ignore entire test files or specific test cases within a suite based on a condition. This condition will be determined by an environment variable. Specifically, you need to ensure that tests in files matching a certain pattern are skipped if a specific environment variable is set.

What needs to be achieved:

Implement a way to ignore test files that match a defined pattern when a particular environment variable is present.

Key requirements:

1. Tests in files with names ending in .integration.test.ts should be ignored if the RUN_INTEGRATION_TESTS environment variable is not set to "true".
2. All other tests should run as normal.

Expected behavior:

• When RUN_INTEGRATION_TESTS is not set or set to any value other than "true", all files ending in .integration.test.ts should be skipped by Jest.
• When RUN_INTEGRATION_TESTS is set to "true", all tests, including those in .integration.test.ts files, should be executed.

Edge cases to consider:

• The environment variable might be missing entirely.
• The environment variable might be set to a value other than "true" (e.g., "false", "yes", "").

Examples

Let's assume the following file structure for our project:

/src
  /calculator
    add.ts
  /users
    user.service.ts
/tests
  __mocks__/
  calculator.test.ts
  calculator.integration.test.ts
  users/
    user.service.test.ts
    user.service.integration.test.ts

Example 1: RUN_INTEGRATION_TESTS is not set

• Environment: process.env.RUN_INTEGRATION_TESTS is undefined.
• Command to run tests: jest
• Expected Output: Jest will report that calculator.integration.test.ts and user.service.integration.test.ts were skipped. The tests in calculator.test.ts and user.service.test.ts will run.
• Explanation: Since RUN_INTEGRATION_TESTS is not "true", Jest's configuration will cause files matching the .integration.test.ts pattern to be ignored.

Example 2: RUN_INTEGRATION_TESTS is set to "false"

• Environment: process.env.RUN_INTEGRATION_TESTS = "false".
• Command to run tests: RUN_INTEGRATION_TESTS="false" jest
• Expected Output: Identical to Example 1. Jest will skip calculator.integration.test.ts and user.service.integration.test.ts.
• Explanation: The condition process.env.RUN_INTEGRATION_TESTS !== "true" is met, leading to the exclusion of integration tests.

Example 3: RUN_INTEGRATION_TESTS is set to "true"

• Environment: process.env.RUN_INTEGRATION_TESTS = "true".
• Command to run tests: RUN_INTEGRATION_TESTS="true" jest
• Expected Output: All tests in all files (calculator.test.ts, calculator.integration.test.ts, user.service.test.ts, user.service.integration.test.ts) will run.
• Explanation: Since RUN_INTEGRATION_TESTS is set to "true", the condition for skipping integration tests is not met, and all tests are executed.

Constraints

• The solution must be implemented using Jest configuration within a jest.config.js or jest.config.ts file.
• The solution should leverage Jest's built-in features for excluding files.
• The approach should be declarative and easy to understand.

Notes

Consider how Jest allows you to specify patterns for files to be included or excluded from the test run. Environment variables are a common way to control conditional behavior in applications and testing environments. You'll need to consult Jest's documentation for options related to test file discovery and exclusion.