Replace `not.toBeEmpty` in two tests

What does this MR do and why?

#toBeEmpty is imported from jQuery and the matcher tests :empty pseudo class (HTML element with not children). Hence, these expectations don't work:

• expect([]).not.toBeEmpty() should fail, but it succeeds
• expect({}).not.toBeEmpty() should fail, but it succeeds

We disallow #toBeEmpty in tests and substitute their usage for alternative approaches:

• expect([].length).toBe(0)
• expect([1].length).toBeGreaterThan(0)

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How to set up and validate locally

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