Creates two unit tests.

README.md

@@ -1,4 +1,4 @@
-## phylotree.js
+# phylotree.js
 
 A JavaScript interactive viewer of [phylogenetic trees](https://en.wikipedia.org/wiki/Phylogenetic_tree), written as an extension of the [D3](http://d3js.org) [hierarchy layout](https://github.com/mbostock/d3/wiki/Hierarchy-Layout). It generates high quality SVG vector graphics, allows a great degree of customizability (CSS or JavaScript callbacks), and comes with a lot of *built-in* convenicence features. 
 
@@ -25,8 +25,12 @@ Key features
 
 1. A [gallery of examples](http://bl.ocks.org/spond) is a good place to learn different ways that phylotree.js can be used to display and annotate the trees. 
 2. A [full-featured web application](http://veg.github.io/phylotree.js/index.html) based on phylotree.js, implemented in [index.html](index.html).
-3. phylotree.js is also used by the 2015 revision of the [datamonkey.org server](http://test.datamonkey.org) for molecular sequence analyis. 
+3. phylotree.js is also used by the 2015 revision of the [datamonkey.org server](http://test.datamonkey.org) for molecular sequence analysis. 
 
 ## Dependencies 
 
 See [bower.json](bower.json) for dependencies. 
+
+## Tests
+
+Run tests using `mocha`.

test.js

@@ -0,0 +1,51 @@
+var path = require("path"),
+  jsdom = require("jsdom"),
+  should = require("should");
+
+describe('Phylotree', function(){
+
+  before(function(done){
+    jsdom.env({
+      file: path.join(__dirname, "index.html"),
+      features: {
+        FetchExternalResources: ["script"],
+        ProcessExternalResources: ["script"]
+      },
+      done: function(err, window){
+        global.window = window;
+        global.tree = window.tree;
+        done();
+      }
+    });
+  });
+
+  it('Create an instance of a tree.', function(){
+    window.should.have.properties('tree');
+  });
+
+  it('Equal scaling factor when invoking spacing functions.', function(){
+    function is_leaf(node){ return node.name && node.name != 'root';}
+    var original_spacing = tree.spacing_y(),
+      original_ys = {},
+      scaling_factor = 0,
+      scaled_coordinates;
+
+    tree.get_nodes().forEach(function(node) {
+        if(is_leaf(node)) original_ys[node.name] = node.y
+    });
+
+    tree.spacing_y(original_spacing/2).update();
+    tree.get_nodes().forEach(node => {
+      if(is_leaf(node) && !scaling_factor){
+        scaling_factor = original_ys[node.name]/node.y;
+        scaling_factor.should.not.be.approximately(1, 1e-1);
+      }
+      if(is_leaf(node)){
+        rescaled_y = scaling_factor*node.y;
+        original_y = original_ys[node.name];
+        rescaled_y.should.be.approximately(original_y, 1e-8);
+      }
+    });
+  });
+
+});