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Data Transformation beginner 8 min

Generate and Check UUIDs for Test Data

Generate UUIDs for fixtures and keep them distinct from meaningful production identifiers.

Scenario

A seed file needs ten user IDs that look like production UUIDs without being production UUIDs. Copying real IDs into fixtures is how customer data leaks into repos, and hand-typing 1234-abcd-... produces values that fail UUID format validation the first time a stricter parser sees them. Generate real v4 UUIDs instead — correctly formatted, random, and guaranteed to mean nothing.

Broken input

Need 10 stable-looking IDs for local seed data

Goal

Use UUID Generator to produce a batch of valid v4 UUIDs for the fixtures. Valid format matters even in test data: a fake ID that fails regex validation tests the validator, not the feature.

Tool sequence

  1. Open UUID Generator.
  2. Set the count to 10 and generate the batch in one go rather than clicking ten times and pasting between other work.
  3. Scan the output shape: 8-4-4-4-12 hex groups, with 4 leading the third group marking version 4.
  4. Confirm no duplicates — vanishingly unlikely with v4, but a copy-paste slip can duplicate a line, and duplicate primary keys make seed scripts fail confusingly.
  5. Paste the batch into the seed file; if fixtures also need matching fake tokens or timestamps, generate those with Random String and Timestamp Converter so nothing in the fixture traces back to production.

Checkpoint output

3f7c2a90-6b1e-4d4a-9c58-2f0e8a71d2b4
b02d91c4-5e77-4c1b-8a3f-64e19d0c7f25
...8 more, all distinct, all version 4

Ten well-formed v4 UUIDs, no duplicates, no relationship to any real account.

Common mistakes

  • Reusing production IDs in local test data — fixtures end up in git history and screenshots.
  • Treating generated UUIDs as sortable or meaningful; v4 values carry no ordering or timestamp.
  • Mixing regenerated-random IDs into tests that assert on stable snapshot values, so the suite fails on every reseed.
  • Hand-editing a generated UUID "to make it memorable" and breaking its version bits.

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