Gemini Interview Reason for rejection

Interviewed at Gemini as Software developer for 4+ hrs + 5hrs of coding challenge take home. Submitted coding challenge on coin-mixer. Got rejected because of weirdest and non sensible reason- ‘tests were not enough’. During interview I ran my app and proved out that its working fine, interviewer said he liked it and also said he like my thought process on future changes. DO NOT WASTE TIME