Prevent invalid arguments entry

Author: Philipp Alferov

index.js

@@ -1,4 +1,5 @@
 'use strict';
+var util = require('util');
 
 function createTree(list, rootNodes) {
   var tree = [];
@@ -33,6 +34,9 @@ function orderByParents(list) {
 }
 
 module.exports = function(obj) {
+  if (!util.isArray(obj)) {
+    throw new Error('Expected an object but got an invalid argument');
+  }
   var cloned = obj.slice();
   var ordered = orderByParents(cloned);
   return createTree(ordered, ordered[0]);

test/test.js

@@ -9,7 +9,7 @@ var current;
 describe('parent pointer array to tree', function() {
   describe('expected behavior', function() {
 
-    beforeEach(function() {
+    before(function() {
       current = toTree(initial);
     });
 
@@ -40,5 +40,17 @@ describe('parent pointer array to tree', function() {
       expect(current).to.be.deep.equal(expected);
     });
 
+  });
+
+  describe('with incorrect arguments', function() {
+    it('should return an empty array if the empty array passed', function() {
+      expect(toTree([])).to.be.deep.equal([]);
+    });
+
+    it('should throw an error if wrong arguments passed', function() {
+      expect(toTree.bind(null, 'string')).to.throw(/invalid argument/);
+      expect(toTree.bind(null, {})).to.throw(/invalid argument/);
+    });
+
   })
 });