When I test a function for revert I do the following in my javascript test file (e.g. myContractTest.js): 

```
const { expect } = require('chai');
const { ethers } = require('hardhat');
const { BigNumber } = require('ethers');

describe('Test contract', () => {
    it('deploy the smart contract and reverts', async () => {
        const MyContract = await ethers.getContractFactory('MyContract');
        const contractInstance = await MyContract.deploy(<add something if you have parameters in the constructor>);
        await expect(contractInstance.myFunction(BigNumber.from('6')))
        .to.revertedWith('Num should be bigger than 5');
    });
});
```
Then Run
```
npx hardhat test --network hardhat ./test/myContractTest.js
```