ava - How import existing class for testing

I am new to ava.

My CalculationUtils is at webapp\a\b\CalculationUtils.js

I put CalculationUtils.test.js in same folder webapp\a\b\CalculationUtils.test.js

My package.json was in webapp.

**How can I test CalculationUtils.addition() in the test file ?**

What I tried

cd webapp
import  add  from 'CalculationUtils .js'; or import  add  from 'Calculation' 
t.is(addition(11, 2017, 3), '2018-2');
test('Current Month 2017Nov add 3 months', t => {
  // t.plan(2);
  t.pass('this assertion passed');
  t.is(addition(11, 2017, 3), '2018-2'); // fails
  t.is(CalculationUtils.addition(11, 2017, 3), '2018-2'); // fails
});

fail reason: Duplicate declaration "addition"

Here is the snippet code of package.json

"scripts": {
   enter code here`"test": "ava a/**/*.test.js --verbose"
};

Thank you.