Open code, practice, and notes →
Download source with English comments · for reading
Playwright · 23 Parallel Execution and Collisions
Series contents · Technology map
Stage: Visual Regression and Execution Strategy · External example · preview instructions · Storage ID: playwright-step-23
Goals and learning outcomes
- Learning outcome: explain the role of Parallelism. Input cases: two tests of the same backup flow.
- Deliverable: file paths and each test’s results. Explain the rationale for handling Independence, linking it to the code.
Prerequisites
Prepare the experiment results for Fixture and Teardown from Unit 22, “Fixtures and Setup Responsibility”.
Key concepts and explanations
Parallelism
Concurrent execution can cause shared filenames to collide. Use output paths specific to the worker or test.
Independence
A test must not depend on data created by a preceding test. It must produce the same result when run alone.
Practice setup
First check the execution scope guidance on the example screen. The following describes the environment needed to extend the assignment in a separate project. Write and run all tests in a separate Node project using @playwright/test and a dedicated local test origin. The existing playwright-01·02·03 previews only display test source; they do not run Playwright in the iframe. Write new test files yourself for the assignments and judge whether they pass only from actual runner output. Do not use a user profile or storage used for everyday work; preserve CSP and isolation.
The linked example is a starting point. It does not implement every task below. Complete work beyond its supported scope in a separate project.
Practice tasks
- In tests/day-23.spec.ts in a separate practice project, separate download paths with testInfo.outputPath and change workers. Refer to the existing Unit 1·14·28 examples only as starting points.
- Input conditions: two tests of the same backup flow. Baseline: 1. Run under the baseline conditions, then record observations and errors in notes/day-23.md.
- Variable: workers; changed value: 2. Run again through the same input path. Deliverable to save: file paths and each test’s results. Hypothesis to check: Keep files and storage from overwriting each other. Compare it with the actual results, and record whether they agree and why they differ.
Variables to observe
| Variable | Baseline | Change | Expected change / hypothesis |
|---|---|---|---|
| workers | 1 | 2 | Keep files and storage from overwriting each other. |
Predictions in this table are not measured results. Change one condition at a time and record why the actual result differs.
Completion criteria
- Required deliverable: file paths and each test’s results. Results are available for both the baseline and changed conditions, allowing comparison of 2 conditions; input values and the execution environment are recorded together.
- The explanation of differences between the two conditions connects both concepts: Parallelism and Independence. For unexpected items, at least 1 cause or reason they remain unresolved is recorded.
Self-check
- Which processing stage does Parallelism affect in this exercise? Input cases: two tests of the same backup flow.
- Variable: workers. Hypothesis to check: Keep files and storage from overwriting each other. Did the actual results agree with the hypothesis? Explain the evidence in terms of Independence.
Official references
- Playwright Installation and Execution
- Playwright Locators
- Playwright Assertions
- Playwright Downloads
- Playwright Visual comparisons
Linked example and execution scope
Example source · Runtime environments and limits
Runnable standalone Playwright spec and HTTP fixture; preview does not run tests.
Source code and records are not overwritten automatically. Resetting an existing example also preserves your notes.
Next learning
Previous: Fixtures and Setup Responsibility · Next: Retries and Flakiness