How can I unit test this node.js module using mocha and chai?

I have this file containing the following code which is the database layer of my api. It is externally dependent on SQL Server to fetch the data.

var sql = require('mssql');
var async = require('async');

module.exports = {
    getDetails: function(number, callback) {

    async.parallel({
            general: function(callback) {
                getGeneral(number, callback);
            },
            preferences: function(callback) {
                getPref(number, callback);
            }
        },
        function(err, results) {
            if (err) {
                logger.error(err);
                throw err;
            }
            callback(results);
        });
}
};

function getGeneral(number, callback) {
    var mainconnection = new sql.Connection(dbCredentials[1].generalDBConfig, function(err) {
        var request = new sql.Request(mainconnection);
        request.input('number', sql.BigInt, number);
        request.execute('[number].[genral_get]', function(err, recordsets) {
            if (err) {
                logger.error(err);
            }
            var gen = {};
            var spResult = recordsets[0];
            if (spResult[0] != null) {
                spResult.forEach(function(record) {
                    var test = {};
                    gen[record.genCode] = record.genValue;
                });

                callback(null, gen);
            } else {
                callback(null, null);
            }

        });

    });
}

function getPref(number, callback) {
    var mainconnection = new sql.Connection(dbCredentials[0].prefDBConfig, function(err) {
        var request = new sql.Request(mainconnection);
        request.input('number', sql.BigInt, number);
        request.execute('[number].[pref_get]', function(err, recordsets) {
            if (err) {
                logger.error(err);
            }
            var spResult = recordsets[0];
            if (spResult[0] != null) {
                callback(null, spResult[0]);
            } else {
                callback(null, null);
            }

        });

    });
}

The database layer return this JSON format data:

{
                        "general": {
                            "number": "72720604"
                            "title": "Mr  ",
                            "buildingNameNumber": null,
                            "subBuildingName": null,
                            "streetName": null,
                            "postalTown": null,
                            "county": null
                        },
                        "pref": {
                            "UseAccessibilitySite": "00000",
                            "IntroductorySource": "75"
                        }
                    };

As I am new to unit testing, I don't know how to start about writing unit tests for this module even though choosing mocha with chai as my unit testing framework. Any kind of suggestions or help is appreciated...