Month in JS Date is 0 indexed so you're referring to 5th June ... so everything's ok.

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console.log(new Date(1970, 5, 5).toDateString())  // Fri Jun 05 1970

Resolving as this is not a kata issue ^{_JustJSThings}

Test.assertEquals(starSign(new Date(1970, 5, 5)), 'Gemini');
5th of May will be Taurus, not Gemini.

That evrywere. JS.

Wrong how?