Adds guard for empty properties in deepEqual when a matcher is provid…

…ed (sinonjs#1901)

In JavaScript every acts like the "for all" quantifier in mathematics.
In particular, for an empty array, it returns true. (It is vacuously
true that all elements of the empty set satisfy any given condition.)

This is not the intended behaviour for deepEqual, we should treat empty
properties as falsy.

Resolves sinonjs#1900

lib/sinon/util/core/deep-equal.js

@@ -38,11 +38,12 @@ var deepEqual = module.exports = function deepEqual(a, b, matcher) {
     }
 
     if (matcher) {
-        var allKeysMatch = every(Object.keys(a), function (key) {
+        var keys = Object.keys(a);
+        var allKeysMatch = every(keys, function (key) {
             return matcher(a[key], b[key]);
         });
 
-        return allKeysMatch;
+        return keys.length > 0 && allKeysMatch;
     }
 
     return false;

test/issues/issues-test.js

@@ -520,4 +520,17 @@ describe("issues", function () {
             stub.restore();
         });
     });
+
+    describe("#1900 - calledWith returns false positive", function () {
+        it("should return false when call args don't match", function () {
+            var spy = sinon.spy();
+            var dateOne = new Date("2018-07-01");
+            var dateTwo = new Date("2018-07-31");
+
+            spy(dateOne);
+
+            var calledWith = spy.calledWith(dateTwo);
+            assert.same(calledWith, false);
+        });
+    });
 });