practice/luhn: fix test

[RaphaelPour]

The test "a simple valid SIN that becomes invalid if reversed" should expect the number to be invalid but does the opposite. I just added the ! for negating the expectation.

Based on the definition of luhn numbers, 059 is invalid as it sums up to 14 which is not evenly divisible by 10.

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[ee7]

I believe this test case is correct as-is, and the test case is defined upstream here.

Based on the definition of luhn numbers, 059 is invalid as it sums up to 14 which is not evenly divisible by 10.

Please double check your understanding of the definition.

For 59, I believe we should check whether 9 + (5*2 - 9) is divisible by 10. It is, and so 59 is valid, right?