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Hardhat is a development environment with the aim to provide all neccessary tools so that you can develop, test and deploy Ethereum software. Truffle and Hardhat are the most famous enviornments for developing Etherum software. Both have their advantages and strenghts, but the trend is, that more and more devs are using Hardhat. Here you can put your tests, scripts, scripts and scripts into your project. Chai is a test-runner and ethers as well as a test for deploying scripts to the ethereum blockchain.