Using same dbname for all test with no instance config

[Sammaye]

module.exports = {
    mongodbMemoryServerOptions: {
        binary: {
            version: '5.0.0',
            skipMD5: true,
        },
        autoStart: false,
        instance: {},
    },

    //useSharedDBForAllJestWorkers: false,
};

I run instance config like this and notice that all dbnames are actually "test".