d3_test_utils.js

const d3SelectionProto = Object.assign({}, d3.selection.prototype);

const D3TestUtils = {
  stubAndForceTransitions() {
    d3.selection.prototype.transition = function() {
      return this;
    };

    d3.selection.prototype.duration = function() {
      return this;
    };

    d3.selection.prototype.delay = function() {
      return this;
    };

    d3.selection.prototype.ease = function() {
      return this;
    };

    d3.selection.prototype.on = function(event, callback) {
      if (event === 'start' || event === 'end') {
        this.each(callback);

        return this;
      } else {
        return d3SelectionProto.on.apply(this, arguments);
      }
    };

    d3.selection.prototype.tween = function(_name, tweenFn) {
      this.each(function(datum, index) {
        tweenFn.call(this, datum, index)(1);
      });

      return this;
    };

    d3.selection.prototype.attrTween = function(attr, tweenFn) {
      this.each(function(datum, index) {
        d3.select(this).attr(attr, tweenFn.call(this, datum, index)(1));
      });

      return this;
    };

    d3.selection.prototype.styleTween = function(style, tweenFn) {
      this.each(function(datum, index) {
        d3.select(this).style(style, tweenFn.call(this, datum, index)(1));
      });

      return this;
    };
  },

  restoreTransitions() {
    d3.selection.prototype = Object.assign({}, d3SelectionProto);
  }
};