# Regular Expressions

> Running Regex101 unit tests against the regex engine Radarr and Sonarr use.

A page from the Profilarr documentation. Web version: https://profilarr.com/docs/regular-expression-testing

TODO: Testing regular expressions with Regex101 unit tests. Covers linking a Regex101 ID, how its unit tests run against the .NET regex engine Radarr and Sonarr use, filtering the results, and two things that catch people out: the tests run against the pattern saved on regex101.com, not the one saved in Profilarr, and results are cached after the first fetch and never refreshed.

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