old_contents: var deviation = require('./');
  var test = require('tape');
  var polygon = require('turf-polygon');
  var point = require('turf-point');
  var featurecollection = require('turf-featurecollection');
  
  test('deviation', function(t){
    var poly1 = polygon([[[0,0],[10,0],[10,10], [0,10]]]);
    var poly2 = polygon([[[10,0],[20,10],[20,20], [20,0]]]);
    var polyFC = featurecollection([poly1, poly2]);
    var pt1 = point(1,1, {population: 500});
    var pt2 = point(1,3, {population: 400});
    var pt3 = point(14,2, {population: 600});
    var pt4 = point(13,1, {population: 500});
    var pt5 = point(19,7, {population: 200}); 
    var ptFC = featurecollection([pt1, pt2, pt3, pt4, pt5]);
  
    var deviated = deviation(polyFC, ptFC, 'population', 'pop_dev');
  
    t.equal(deviated.features[0].geometry.type, 'Polygon');
    t.equal(deviated.features[0].properties.pop_dev, 50);
  
    t.end();
  });
new_contents: var deviation = require('./');
  var test = require('tape');
  var polygon = require('turf-polygon');
  var point = require('turf-point');
  var featurecollection = require('turf-featurecollection');
  
  test('deviation', function(t){
    var poly1 = polygon([[[0,0],[10,0],[10,10],[0,10],[0,0]]]);
    var poly2 = polygon([[[10,0],[20,10],[20,20],[20,0],[10,0]]]);
    var polyFC = featurecollection([poly1, poly2]);
    var pt1 = point(1,1, {population: 500});
    var pt2 = point(1,3, {population: 400});
    var pt3 = point(14,2, {population: 600});
    var pt4 = point(13,1, {population: 500});
    var pt5 = point(19,7, {population: 200}); 
    var ptFC = featurecollection([pt1, pt2, pt3, pt4, pt5]);
  
    var deviated = deviation(polyFC, ptFC, 'population', 'pop_dev');
  
    t.equal(deviated.features[0].geometry.type, 'Polygon');
    t.equal(deviated.features[0].properties.pop_dev, 50);
  
    t.end();
  });
  
subject: Fix polygons in test.js