XUnit reporter should handle exceptions during diff generation (#4068)

Author: rgroothuijsen

lib/reporters/base.js

@@ -154,14 +154,14 @@ exports.cursor = {
   }
 };
 
-function showDiff(err) {
+var showDiff = (exports.showDiff = function(err) {
   return (
     err &&
     err.showDiff !== false &&
     sameType(err.actual, err.expected) &&
     err.expected !== undefined
   );
-}
+});
 
 function stringifyDiffObjs(err) {
   if (!utils.isString(err.actual) || !utils.isString(err.expected)) {
@@ -182,9 +182,19 @@ function stringifyDiffObjs(err) {
  * @return {string} Diff
  */
 var generateDiff = (exports.generateDiff = function(actual, expected) {
-  return exports.inlineDiffs
-    ? inlineDiff(actual, expected)
-    : unifiedDiff(actual, expected);
+  try {
+    return exports.inlineDiffs
+      ? inlineDiff(actual, expected)
+      : unifiedDiff(actual, expected);
+  } catch (err) {
+    var msg =
+      '\n      ' +
+      color('diff added', '+ expected') +
+      ' ' +
+      color('diff removed', '- actual:  failed to generate Mocha diff') +
+      '\n';
+    return msg;
+  }
 });
 
 /**

lib/reporters/xunit.js

@@ -163,9 +163,9 @@ XUnit.prototype.test = function(test) {
   if (test.state === STATE_FAILED) {
     var err = test.err;
     var diff =
-      Base.hideDiff || !err.actual || !err.expected
-        ? ''
-        : '\n' + Base.generateDiff(err.actual, err.expected);
+      !Base.hideDiff && Base.showDiff(err)
+        ? '\n' + Base.generateDiff(err.actual, err.expected)
+        : '';
     this.write(
       tag(
         'testcase',

test/reporters/xunit.spec.js

@@ -350,6 +350,42 @@ describe('XUnit reporter', function() {
           '</failure></testcase>';
         expect(expectedWrite, 'to be', expectedTag);
       });
+
+      it('should handle non-string diff values', function() {
+        var runner = new EventEmitter();
+        createStatsCollector(runner);
+        var xunit = new XUnit(runner);
+
+        var expectedTest = {
+          state: STATE_FAILED,
+          title: expectedTitle,
+          parent: {
+            fullTitle: function() {
+              return expectedClassName;
+            }
+          },
+          duration: 1000,
+          err: {
+            actual: 1,
+            expected: 2,
+            message: expectedMessage,
+            stack: expectedStack
+          }
+        };
+
+        sandbox.stub(xunit, 'write').callsFake(function(str) {
+          expectedWrite += str;
+        });
+
+        runner.emit(EVENT_TEST_FAIL, expectedTest, expectedTest.err);
+        runner.emit(EVENT_RUN_END);
+        sandbox.restore();
+
+        var expectedDiff =
+          '\n      + expected - actual\n\n      -1\n      +2\n      ';
+
+        expect(expectedWrite, 'to contain', expectedDiff);
+      });
     });
 
     describe('on test pending', function() {