Warn of potential memory leaks

docs/release-source/release/sandbox.md

@@ -334,3 +334,7 @@ Verifies all mocks created through the sandbox.
 #### `sandbox.verifyAndRestore();`
 
 Verifies all mocks and restores all fakes created through the sandbox.
+
+#### `sandbox.leakThreshold`
+
+Gets/sets the threshold at which memory leak detection warnings are logged.

lib/sinon/sandbox.js

@@ -1,6 +1,7 @@
 "use strict";
 
 var arrayProto = require("@sinonjs/commons").prototypes.array;
+var logger = require("@sinonjs/commons").deprecated;
 var collectOwnMethods = require("./collect-own-methods");
 var getPropertyDescriptor = require("./util/core/get-property-descriptor");
 var isPropertyConfigurable = require("./util/core/is-property-configurable");
@@ -16,6 +17,8 @@ var fakeServer = require("nise").fakeServer;
 var fakeXhr = require("nise").fakeXhr;
 var usePromiseLibrary = require("./util/core/use-promise-library");
 
+var DEFAULT_LEAK_THRESHOLD = 10000;
+
 var filter = arrayProto.filter;
 var forEach = arrayProto.forEach;
 var push = arrayProto.push;
@@ -33,10 +36,26 @@ function applyOnEach(fakes, method) {
 
 function Sandbox() {
     var sandbox = this;
-    var collection = [];
     var fakeRestorers = [];
     var promiseLib;
 
+    var collection = [];
+    var loggedLeakWarning = false;
+    sandbox.leakThreshold = DEFAULT_LEAK_THRESHOLD;
+
+    function addToCollection(object) {
+        if (
+            push(collection, object) > sandbox.leakThreshold &&
+            !loggedLeakWarning
+        ) {
+            // eslint-disable-next-line no-console
+            logger.printWarning(
+                "Potential memory leak detected; be sure to call restore() to clean up your sandbox. To suppress this warning, modify the leakThreshold property of your sandbox."
+            );
+            loggedLeakWarning = true;
+        }
+    }
+
     sandbox.assert = sinonAssert.createAssertObject();
 
     sandbox.serverPrototype = fakeServer;
@@ -57,7 +76,7 @@ function Sandbox() {
         var ownMethods = collectOwnMethods(stubbed);
 
         forEach(ownMethods, function (method) {
-            push(collection, method);
+            addToCollection(method);
         });
 
         usePromiseLibrary(promiseLib, ownMethods);
@@ -115,7 +134,7 @@ function Sandbox() {
     sandbox.mock = function mock() {
         var m = sinonMock.apply(null, arguments);
 
-        push(collection, m);
+        addToCollection(m);
         usePromiseLibrary(promiseLib, m);
 
         return m;
@@ -348,12 +367,12 @@ function Sandbox() {
             var ownMethods = collectOwnMethods(spy);
 
             forEach(ownMethods, function (method) {
-                push(collection, method);
+                addToCollection(method);
             });
 
             usePromiseLibrary(promiseLib, ownMethods);
         } else {
-            push(collection, spy);
+            addToCollection(spy);
             usePromiseLibrary(promiseLib, spy);
         }
 
@@ -374,7 +393,7 @@ function Sandbox() {
     sandbox.fake = function fake(f) {
         var s = sinonFake.apply(sinonFake, arguments);
 
-        push(collection, s);
+        addToCollection(s);
 
         return s;
     };
@@ -385,7 +404,7 @@ function Sandbox() {
             sandbox.fake[key] = function () {
                 var s = fakeBehavior.apply(fakeBehavior, arguments);
 
-                push(collection, s);
+                addToCollection(s);
 
                 return s;
             };
@@ -396,7 +415,7 @@ function Sandbox() {
         var clock = sinonClock.useFakeTimers.call(null, args);
 
         sandbox.clock = clock;
-        push(collection, clock);
+        addToCollection(clock);
 
         return clock;
     };
@@ -429,14 +448,14 @@ function Sandbox() {
         }
 
         sandbox.server = proto.create();
-        push(collection, sandbox.server);
+        addToCollection(sandbox.server);
 
         return sandbox.server;
     };
 
     sandbox.useFakeXMLHttpRequest = function useFakeXMLHttpRequest() {
         var xhr = fakeXhr.useFakeXMLHttpRequest();
-        push(collection, xhr);
+        addToCollection(xhr);
         return xhr;
     };
 

test/sandbox-test.js

@@ -134,6 +134,51 @@ describe("Sandbox", function () {
 
             assert.equals(fakes.length, 2);
         });
+
+        describe("warns of potential leak when", function () {
+            var warn;
+
+            beforeEach(function () {
+                warn = this.sandbox.stub(deprecated, "printWarning");
+            });
+
+            afterEach(function () {
+                warn.restore();
+            });
+
+            it("many fakes are created", function () {
+                assert.equals(typeof this.sandbox.leakThreshold, "number");
+
+                createTooManyFakes(this.sandbox);
+
+                assert(warn.called);
+            });
+
+            it("a configurable number of fakes are created", function () {
+                this.sandbox.leakThreshold = 20;
+
+                createTooManyFakes(this.sandbox);
+
+                assert(warn.called);
+            });
+
+            it("a leak warning has not already been output", function () {
+                this.sandbox.leakThreshold = 20;
+
+                createTooManyFakes(this.sandbox);
+                this.sandbox.restore();
+                warn.resetHistory();
+
+                createTooManyFakes(this.sandbox);
+                assert(!warn.called);
+            });
+
+            function createTooManyFakes(sandbox) {
+                for (var i = 0; i < sandbox.leakThreshold; i++) {
+                    sandbox.spy();
+                }
+            }
+        });
     });
 
     describe(".spy", function () {