Please check if the PR fulfills these requirements

• The PR has no duplicates (please search among the Pull Requests
  before creating one)
• The PR follows
  our contributing guidelines
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)
• UPGRADING.md has been updated with a migration guide (for breaking changes)

• What kind of change does this PR introduce?

Fixes failing tests.

• What is the current behavior?

Tests are failing because the number of cores in the index is changed.

• What is the new behavior?

Tests won't fail anymore since the expected number of cores is not a fixed number.

• Does this PR introduce a breaking change, and is
  titled accordingly?

Nope.

• Other information:

None.

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