Parallel Test Execution with TestNG
Why Run Tests in Parallel?
As test suites grow, running them one after another becomes slow. Parallel execution runs multiple tests simultaneously, dramatically reducing total execution time - especially valuable in CI/CD pipelines.
Configuring Parallel Execution in TestNG
TestNG supports parallel execution directly through its XML configuration file, where you can specify whether to parallelize at the method, class, or test-suite level, along with the thread count to use.
- parallel="methods" - runs individual test methods in parallel
- parallel="classes" - runs entire test classes in parallel
- thread-count - controls how many tests run simultaneously
Parallel Execution Levels
| Level | Best For |
|---|---|
| Methods | Maximum speed when tests are fully independent |
| Classes | Grouping related tests while still parallelizing across groups |
| Tests (suite) | Running entirely separate test suites side by side |
Best Practices for Reliable Parallel Runs
Parallel execution only works reliably when tests are fully independent of one another - avoid shared state, use separate browser instances per thread, and ensure test data doesn't collide between simultaneously running tests.
That completes the automation-execution side of things - next, let's look beyond the UI at API testing, which often complements Selenium in a complete test strategy.
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