Resolution method is overspecified when testing with Mocha and Supertest for Node.js

Question

I have the following endpoint for validating a JSON file and I am using an integration test for the same. I use Mocha for testing and the code is as follows:

    const request = require('supertest');
    const app = require('../..//app.js');
    
     describe.only('GET /validate', function() {
        it('Return pricing file validation result', function(done) {
            return request(app)
                .get('/api/validate')
                .expect(200)
                .expect('Content-Type',/json/)
                .expect('{"status":"success","message":"Pricing file validation completed successfully"}')
                .end(function(err, res) {
                    if (err) return done(err);
                    done();
                });
        })
    })

and the endpoint is mapped to :

export const validatePricing =  (req, res) => {
    validatePricingFile('./pricing_qa.json').then(r =>{
        res.status(200).json({
            status:"success",
            message: 'Pricing file validation completed successfully'
        })
    }).catch(error=>{
        console.log(error)
        res.status(422).json({
            'status':"error",
            message: error.message
        })
    })
}

The validatePricingFile returns a promise as follows:

return new Promise((resolve, reject) => {
    const ajValidator = new ajv({allErrors: true});
    const validate = ajValidator.compile(pricingSchema);
    const valid = validate(pricingData);
    if (!valid) {
        return reject({
            message:validate.errors
         })
    } else {
        resolve(true)
    }
})

When I run the test, I am getting the following error:

Error: Resolution method is overspecified. Specify a callback *or* return a Promise; not both. How can I fix this and run the tests ?