[Breaking] ensure Error objects compare properly

.eslintrc

@@ -16,6 +16,7 @@
       "files": ["example/**", "test/**"],
       "rules": {
         "array-bracket-newline": 0,
+        "max-lines": 0,
         "max-params": 0,
         "max-statements": 0,
         "no-console": 0,

index.js

@@ -50,7 +50,7 @@ function isBuffer(x) {
 }
 
 function objEquiv(a, b, opts) {
-  /* eslint max-statements: [2, 50] */
+  /* eslint max-statements: [2, 70] */
   var i, key;
   if (typeof a !== typeof b) { return false; }
   if (isUndefinedOrNull(a) || isUndefinedOrNull(b)) { return false; }
@@ -60,6 +60,14 @@ function objEquiv(a, b, opts) {
 
   if (isArguments(a) !== isArguments(b)) { return false; }
 
+  // TODO: replace when a cross-realm brand check is available
+  var aIsError = a instanceof Error;
+  var bIsError = b instanceof Error;
+  if (aIsError !== bIsError) { return false; }
+  if (aIsError || bIsError) {
+    if (a.name !== b.name || a.message !== b.message) { return false; }
+  }
+
   var aIsRegex = isRegex(a);
   var bIsRegex = isRegex(b);
   if (aIsRegex !== bIsRegex) { return false; }

test/cmp.js

@@ -342,3 +342,11 @@ test('functions', function (t) {
 
   t.end();
 });
+
+test('Errors', function (t) {
+  t.deepEqualTest(new Error('xyz'), new Error('xyz'), 'two errors of the same type with the same message', true, true, false);
+  t.deepEqualTest(new Error('xyz'), new TypeError('xyz'), 'two errors of different types with the same message', false, false);
+  t.deepEqualTest(new Error('xyz'), new Error('zyx'), 'two errors of the same type with a different message', false, false);
+
+  t.end();
+});