Faster Feedback Loops: Running Tests on Git Changes

Long test suite run times can significantly slow down development. Running the entire suite for every change, especially in larger projects, becomes inefficient. A focused approach that executes only the tests relevant to the modified code provides quicker feedback and accelerates the development cycle.

The Challenge: Identifying Relevant Tests

The primary challenge lies in accurately determining which tests are affected by a particular code change. A naive approach of simply running all tests is slow, while manually selecting tests is error-prone and unsustainable. Automating this process requires a system that can analyze code modifications and map them to corresponding tests.

The Solution: Targeted Test Execution Based on Git Diff

By analyzing the changes introduced by a commit using git diff, we can identify the modified files. This information is then used to determine which tests need to be executed. The mapping from files to tests can be achieved through several strategies:

• Direct Naming Convention: If tests are named consistently with the files they test (e.g., MyClass.php and MyClassTest.php), the mapping is straightforward.
• Use-Statement Reverse Indexing: By analyzing the use statements in the modified files, we can identify the classes and interfaces that are being used. Tests that depend on these classes should then be executed.
• Special-Case Rules: Specific file types, such as migrations or factories, often have well-defined test dependencies. For example, modifying a database migration typically requires running integration tests that verify the database schema.

Here's an illustrative example of how you might implement this in a PHP environment:

// Example: Determine relevant tests based on modified files

$modifiedFiles = shell_exec('git diff --name-only --diff-filter=AM HEAD^ HEAD');
$modifiedFiles = explode("\n", trim($modifiedFiles));

$testsToRun = [];

foreach ($modifiedFiles as $file) {
    if (strpos($file, 'src/') === 0) {
        // Map source files to their corresponding test files
        $testFile = str_replace('src/', 'tests/', $file);
        $testFile = str_replace('.php', 'Test.php', $testFile);
        if (file_exists($testFile)) {
            $testsToRun[] = $testFile;
        }
    } elseif (strpos($file, 'migrations/') === 0) {
        // Always run database integration tests for migration changes
        $testsToRun[] = 'tests/Integration/DatabaseTest.php';
    }
}

// Execute the identified tests
$testCommand = './vendor/bin/phpunit ' . implode(' ', $testsToRun);
shell_exec($testCommand);

Integration into the CI/CD Pipeline

This targeted test execution approach can be seamlessly integrated into a CI/CD pipeline. By replacing the full test suite execution with this optimized process, the feedback loop is significantly shortened, allowing developers to identify and fix issues more quickly.

Conclusion

Implementing a system that runs tests based on git diff provides faster feedback during development. By employing direct naming conventions, use-statement analysis, and special-case rules, you can effectively map code changes to relevant tests. This optimization accelerates the development cycle and improves overall productivity.