diff --git a/lib/reporters/base.js b/lib/reporters/base.js
index f3a4e67ca3..b552e09756 100644
--- a/lib/reporters/base.js
+++ b/lib/reporters/base.js
@@ -166,6 +166,25 @@ function stringifyDiffObjs (err) {
   }
 }
 
+/**
+ * Returns a diff between 2 strings with coloured ANSI output.
+ *
+ * The diff will be either inline or unified dependant on the value
+ * of `Base.inlineDiff`.
+ *
+ * @api private
+ * @param {String} actual
+ * @param {String} expected
+ * @return {string} Diff
+ */
+var generateDiff = exports.generateDiff = function (actual, expected) {
+  if (exports.inlineDiffs) {
+    return inlineDiff(actual, expected);
+  } else {
+    return unifiedDiff(actual, expected);
+  }
+};
+
 /**
  * Output the given `failures` as a list.
  *
@@ -215,11 +234,7 @@ exports.list = function (failures) {
       var match = message.match(/^([^:]+): expected/);
       msg = '\n      ' + color('error message', match ? match[1] : msg);
 
-      if (exports.inlineDiffs) {
-        msg += inlineDiff(err);
-      } else {
-        msg += unifiedDiff(err);
-      }
+      msg += generateDiff(err.actual, err.expected);
     }
 
     // indent stack trace
@@ -368,14 +383,15 @@ function pad (str, len) {
 }
 
 /**
- * Returns an inline diff between 2 strings with coloured ANSI output
+ * Returns an inline diff between 2 strings with coloured ANSI output.
  *
  * @api private
- * @param {Error} err with actual/expected
+ * @param {String} actual
+ * @param {String} expected
  * @return {string} Diff
  */
-function inlineDiff (err) {
-  var msg = errorDiff(err);
+function inlineDiff (actual, expected) {
+  var msg = errorDiff(actual, expected);
 
   // linenos
   var lines = msg.split('\n');
@@ -401,13 +417,14 @@ function inlineDiff (err) {
 }
 
 /**
- * Returns a unified diff between two strings.
+ * Returns a unified diff between two strings with coloured ANSI output.
  *
  * @api private
- * @param {Error} err with actual/expected
+ * @param {String} actual
+ * @param {String} expected
  * @return {string} The diff.
  */
-function unifiedDiff (err) {
+function unifiedDiff (actual, expected) {
   var indent = '      ';
   function cleanUp (line) {
     if (line[0] === '+') {
@@ -427,7 +444,7 @@ function unifiedDiff (err) {
   function notBlank (line) {
     return typeof line !== 'undefined' && line !== null;
   }
-  var msg = diff.createPatch('string', err.actual, err.expected);
+  var msg = diff.createPatch('string', actual, expected);
   var lines = msg.split('\n').splice(5);
   return '\n      ' +
     colorLines('diff added', '+ expected') + ' ' +
@@ -440,11 +457,12 @@ function unifiedDiff (err) {
  * Return a character diff for `err`.
  *
  * @api private
- * @param {Error} err
- * @return {string}
+ * @param {String} actual
+ * @param {String} expected
+ * @return {string} the diff
  */
-function errorDiff (err) {
-  return diff.diffWordsWithSpace(err.actual, err.expected).map(function (str) {
+function errorDiff (actual, expected) {
+  return diff.diffWordsWithSpace(actual, expected).map(function (str) {
     if (str.added) {
       return colorLines('diff added', str.value);
     }