diff --git a/mocha.opts b/mocha.opts
new file mode 100644
index 0000000..3b7d97b
--- /dev/null
+++ b/mocha.opts
@@ -0,0 +1,3 @@
+--reporter spec
+--bail
+--check-leaks
diff --git a/test.js b/test.js
new file mode 100644
index 0000000..2a74e1b
--- /dev/null
+++ b/test.js
@@ -0,0 +1,95 @@
+var expect = require('expect.js');
+var arrayDiff = require('./index');
+var InsertDiff = arrayDiff.InsertDiff;
+var RemoveDiff = arrayDiff.RemoveDiff;
+var MoveDiff = arrayDiff.MoveDiff;
+
+function insert(array, index, values) {
+  array.splice.apply(array, [index, 0].concat(values));
+}
+
+function remove(array, index, howMany) {
+  return array.splice(index, howMany);
+}
+
+function move(array, from, to, howMany) {
+  var values = remove(array, from, howMany);
+  insert(array, to, values);
+}
+
+function applyDiff(before, diff) {
+  var out = before.slice();
+  for (var i = 0; i < diff.length; i++) {
+    var item = diff[i];
+    // console.log 'applying:', out, item
+    if (item instanceof InsertDiff) {
+      insert(out, item.index, item.values);
+    } else if (item instanceof RemoveDiff) {
+      remove(out, item.index, item.howMany);
+    } else if (item instanceof MoveDiff) {
+      move(out, item.from, item.to, item.howMany);
+    }
+  }
+  return out;
+}
+
+function randomWhole(max) {
+  return Math.floor(Math.random() * (max + 1));
+}
+
+function randomArray(maxLength, maxValues) {
+  if (maxLength == null) maxLength = 20;
+  if (maxValues == null) maxValues = maxLength;
+  var results = [];
+  for (var i = randomWhole(maxLength); i--;) {
+    results.push(randomWhole(maxValues));
+  }
+  return results;
+}
+
+function testDiff(before, after, equalFn) {
+  // console.log()
+  // console.log 'before =', before
+  // console.log 'after =', after
+  var diff = arrayDiff(before, after, equalFn);
+  var expected = applyDiff(before, diff);
+  expect(expected).to.eql(after);
+}
+
+describe('arrayDiff', function() {
+
+  it('diffs empty arrays', function() {
+    testDiff([], []);
+    testDiff([], [0, 1, 2]);
+    testDiff([0, 1, 2], []);
+  });
+
+  it('supports custom equality comparisons', function() {
+    var before = [{id: 1}, {id: 2}];
+    var after = [{id: 1}];
+    testDiff(before, after, function(a, b) {
+      return a.id === b.id;
+    });
+  });
+
+  it('diffs randomly rearranged arrays of numbers', function() {
+    function randomSort() {
+      return Math.random() - 0.5;
+    }
+    for (var i = 1000; i--;) {
+      // before = [0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19]
+      var before = randomArray(50);
+      var after = before.slice().sort(randomSort);
+      testDiff(before, after);
+    }
+  });
+
+  it('diffs random arrays of numbers', function() {
+    for (var i = 1000; i--;) {
+      var before = randomArray(50, 20);
+      var after = randomArray(50, 20);
+      testDiff(before, after);
+    }
+  });
+
+});
diff --git a/test/test.mocha.coffee b/test/test.mocha.coffee
deleted file mode 100644
index d82092c..0000000
--- a/test/test.mocha.coffee
+++ /dev/null
@@ -1,69 +0,0 @@
-expect = require 'expect.js'
-arrayDiff = require '../index'
-
-{InsertDiff, RemoveDiff, MoveDiff} = arrayDiff
-
-insert = (array, index, values) ->
-  array.splice.apply array, [index, 0].concat(values)
-remove = (array, index, howMany) ->
-  array.splice index, howMany
-move = (array, from, to, howMany) ->
-  values = remove array, from, howMany
-  insert array, to, values
-
-applyDiff = (before, diff) ->
-  out = before.slice()
-  for item in diff
-    # console.log 'applying:', out, item
-    if item instanceof InsertDiff
-      insert out, item.index, item.values
-    else if item instanceof RemoveDiff
-      remove out, item.index, item.howMany
-    else if item instanceof MoveDiff
-      move out, item.from, item.to, item.howMany
-  return out
-
-randomWhole = (max) ->
-  Math.floor Math.random() * (max + 1)
-
-randomArray = (maxLength = 20, maxValues = maxLength) ->
-  i = randomWhole maxLength
-  return (randomWhole maxValues while i--)
-
-testDiff = (before, after, equalFn) ->
-  # console.log()
-  # console.log 'before =', before
-  # console.log 'after =', after
-  diff = arrayDiff before, after, equalFn
-  expected = applyDiff before, diff
-  expect(expected).to.eql after
-
-describe 'arrayDiff', ->
-
-  it 'diffs empty arrays', ->
-    testDiff [], []
-    testDiff [], [0, 1, 2]
-    testDiff [0, 1, 2], []
-
-  it 'supports custom equality comparisons', ->
-    before = [{id: 1}, {id: 2}]
-    after = [{id: 1}]
-    testDiff before, after, (a, b) ->
-      return a.id is b.id
-
-  it 'diffs randomly rearranged arrays of numbers', ->
-    i = 1000
-    while i--
-      # before = [0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19]
-      before = randomArray 50
-      after = before.slice().sort(-> Math.random() - 0.5)
-      testDiff before, after
-    return
-
-  it "diffs random arrays of numbers", ->
-    i = 1000
-    while i--
-      before = randomArray 50, 20
-      after = randomArray 50, 20
-      testDiff before, after
-    return