assert: var -> const and added tests

Cleaned up as per comments in issue

Ref: nodejs#6416

lib/assert.js

@@ -268,7 +268,7 @@ function _deepEqual(actual, expected, strict, memos) {
   // a) The same number of owned enumerable properties
   // b) The same set of keys/indexes (although not necessarily the same order)
   // c) Equivalent values for every corresponding key/index
-  // d) For Maps, strict-equal keys mapping to deep-equal values
+  // d) For Sets and Maps, equal contents
   // Note: this accounts for both named and indexed properties on Arrays.
 
   // Use memos to handle cycles.
@@ -291,22 +291,20 @@ function setEquiv(a, b, strict, actualVisitedObjects) {
   //   assert.deepEqual(new Set(['1', 1]), new Set([1]))
   //
   // In theory, all the items in the first set have a corresponding == value in
-  // the second set, but the sets have different sizes. Should they be
-  // considered to be non-strict deep equal to one another? Its a silly case,
+  // the second set, but the sets have different sizes. Its a silly case,
   // and more evidence that deepStrictEqual should always be preferred over
-  // deepEqual. The implementation currently returns false, which is a simpler
-  // and faster implementation.
+  // deepEqual. The implementation currently returns false, which is simpler
+  // and slightly faster.
   if (a.size !== b.size)
     return false;
 
-  var val1, val2;
-  outer: for (val1 of a) {
+  outer: for (const val1 of a) {
     if (!b.has(val1)) {
       // The value doesn't exist in the second set by reference, so we'll go
       // hunting for something thats deep-equal to it. Note that this is O(n^2)
       // complexity, and will get slower if large, very similar sets / maps are
       // nested inside. Unfortunately there's no real way around this.
-      for (val2 of b) {
+      for (const val2 of b) {
         if (_deepEqual(val1, val2, strict, actualVisitedObjects)) {
           continue outer;
         }
@@ -328,8 +326,7 @@ function mapEquiv(a, b, strict, actualVisitedObjects) {
   if (a.size !== b.size)
     return false;
 
-  var key1, key2, item1, item2;
-  outer: for ([key1, item1] of a) {
+  outer: for (const [key1, item1] of a) {
     // To be able to handle cases like:
     //   Map([[1, 'a'], ['1', 'b']]) vs Map([['1', 'a'], [1, 'b']])
     // or:
@@ -346,7 +343,7 @@ function mapEquiv(a, b, strict, actualVisitedObjects) {
 
     // Hunt for keys which are deep-equal to key1 in b. Just like setEquiv
     // above, this hunt makes this function O(n^2).
-    for ([key2, item2] of b) {
+    for (const [key2, item2] of b) {
       // Just for performance. We already checked these keys above.
       if (key2 === key1)
         continue;

test/parallel/test-assert-deep.js

@@ -245,4 +245,25 @@ assert.throws(() =>
   assertNotDeepOrStrict(m1, m2);
 }
 
+{
+  // Circular references.
+  const s1 = new Set();
+  s1.add(s1);
+  const s2 = new Set();
+  s2.add(s2);
+  assertDeepAndStrictEqual(s1, s2);
+
+  const m1 = new Map();
+  m1.set(2, m1);
+  const m2 = new Map();
+  m2.set(2, m2);
+  assertDeepAndStrictEqual(m1, m2);
+
+  const m3 = new Map();
+  m3.set(m3, 2);
+  const m4 = new Map();
+  m4.set(m4, 2);
+  assertDeepAndStrictEqual(m3, m4);
+}
+
 /* eslint-enable */