test(offline): fixing offline dc tests

[mikeringrose]

Description

Correcting the test data to include the country in the description. Changing the difference calculation delta for doubles.

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Checklist

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [x] I have updated the CHANGELOG including this PR (where applicable)
• [x] I have run tests and automatic checks locally
• [x] I have run pitest check locally and checked that the coverage increased (or didn't change) or decreased insignificantly
• [x] I have made corresponding changes to the documentation (where applicable)
• [x] I have grouped commits logically or I promise to squash my commits before merge