Is it possible to access tested function scope using sinon?

Let's assume I have the following test file:

import sinon from 'sinon';

function testFunction (param) {
  const sum = param + 1;
}

describe('testFunction', () => {
  it('increase the parameter value', () => {
    const testFunctionSpy = sinon.spy(testFunction);

    testFunctionSpy(2);

    //expect sum to be equal 3    

  })
});

Is it possible to access the scope of the testFunction, the value of sum variable in particular?