d3_circles_test.js

/* Implementation */

function renderCircles(xScale, yScale, data) {
  d3.selectAll('circle')
    .data(data)
    .enter()
    .append('circle')
      .attr('cx', circleCX.bind(undefined, xScale)
      .attr('cy', circleCY.bind(undefined, yScale);
}

function circleCX(xScale, datum) {
  return xScale(datum.x);
}

function circleCY(yScale, datum) {
  return yScale(datum.y);
}

/* Test */

describe('#circleCX', function() {
  it('returns the correct values', function() {
    var xScale = d3.scale.linear().domain([0, 10]).range([0, 100]);
    assert.strictEqual(circleCX(xScale, { x: 0, y: 0 }), 0);
    assert.strictEqual(circleCX(xScale, { x: 5, y: 0 }), 50);
    assert.strictEqual(circleCX(xScale, { x: 9.9, y: 0 }), 99);
    assert.strictEqual(circleCX(xScale, { x: 10, y: 0 }), 100);
  });
});