{
    "env": {
        "mocha": true
    },
    "rules": {
        "import/no-extraneous-dependencies": [2, {
            "devDependencies": true
        }]
    }
}

{
    "env": {
        "mocha": true
    },
    "rules": {
        "no-unused-expressions"             : ["off"],
        "import/no-extraneous-dependencies" : [2, { "devDependencies": true }]
    }
}

Disable the `no-unused-expressions` eslint rule for unit-tests
Disable the `no-unused-expressions` eslint rule for unit-tests
