Fake Data

The fake-data arbitraries produce values that look like production data: UUIDs, email addresses, IPv4/IPv6, URLs, filenames, MIME types. Each one is a convenience wrapper built on top of primitives and composites, pre-configured so that generated values satisfy a recognisable format.

Reach for them when your code branches on the shape of its input — a regex that expects a valid email, a parser that only accepts well-formed URLs, a router that inspects filename extensions. Feeding such code a plain fc.string() would spend almost every run in the error path and tell you nothing about the happy path you actually care about.

:::warning Do not over-use fake data Fake-data arbitraries have narrower shrink spaces than primitives: a shrunk counterexample for fc.emailAddress() is still a valid email, not an empty string. When your code does not care about the format, plain primitives give better coverage and tighter counterexamples. Use fake data to unblock a specific branch, not as a default. :::

📄️File

Generate file content values.

📄️Identifier

Generate identifier values.

📄️Internet

Generate internet related values.