Prohibit faking of faked timers

src/fake-timers-src.js

@@ -1,6 +1,7 @@
 "use strict";
 
 const globalObject = require("@sinonjs/commons").global;
+const globalDate = globalObject.Date;
 
 /**
  * @typedef {object} IdleDeadline
@@ -133,6 +134,7 @@ const globalObject = require("@sinonjs/commons").global;
  * @returns {FakeTimers}
  */
 function withGlobal(_global) {
+    const stockDate = _global.Date;
     const userAgent = _global.navigator && _global.navigator.userAgent;
     const isRunningInIE = userAgent && userAgent.indexOf("MSIE ") > -1;
     const maxTimeout = Math.pow(2, 31) - 1; //see https://heycam.github.io/webidl/#abstract-opdef-converttoint
@@ -1635,6 +1637,16 @@ function withGlobal(_global) {
             );
         }
 
+        if (
+            typeof stockDate === "function" &&
+            Math.abs(new Date().getTime() - new stockDate().getTime()) > 100
+        ) {
+            // Allow 100 ms variance for determining already faked timers.
+            // Timers are already faked; this is a problem.
+            // Make the user reset timers before continuing.
+            throw new TypeError("Can't fake timers twice.");
+        }
+
         // eslint-disable-next-line no-param-reassign
         config = typeof config !== "undefined" ? config : {};
         config.shouldAdvanceTime = config.shouldAdvanceTime || false;

test/fake-timers-test.js

@@ -53,6 +53,69 @@ const utilPromisifyAvailable = promisePresent && utilPromisify;
 const timeoutResult = global.setTimeout(NOOP, 0);
 const addTimerReturnsObject = typeof timeoutResult === "object";
 
+describe("issue #2449: perminent loss of native functions", () => {
+    it("should not fake faked timers", () => {
+        const currentTime = new Date().getTime();
+        const date1 = new Date("2015-09-25");
+        const date2 = new Date("2015-09-26");
+        let clock = FakeTimers.install({ now: date1 });
+        assert.same(clock.now, date1.getTime());
+        assert.same(new Date().getTime(), 1443139200000);
+        assert.exception(function () {
+            FakeTimers.install({ now: date2 });
+        });
+        clock.uninstall();
+        clock = FakeTimers.install({ now: date2 });
+        assert.same(clock.now, date2.getTime());
+        clock.uninstall();
+        assert.greater(new Date().getTime(), currentTime, true);
+    });
+
+    it("should not fake faked timers on a custom target", () => {
+        const setTimeoutFake = sinon.fake();
+        const context = {
+            Date: Date,
+            setTimeout: setTimeoutFake,
+            clearTimeout: sinon.fake(),
+        };
+        let clock = FakeTimers.withGlobal(context).install();
+        assert.equals(setTimeoutFake.callCount, 1);
+        clock.setTimeout(NOOP, 0);
+        assert.equals(setTimeoutFake.callCount, 1);
+        assert.exception(function () {
+            clock = FakeTimers.withGlobal(context).install();
+        });
+        clock.uninstall();
+    });
+
+    it("should allow a fake on a custom target if the global is faked", () => {
+        const globalClock = FakeTimers.install();
+        const setTimeoutFake = sinon.fake();
+        const context = {
+            Date: Date,
+            setTimeout: setTimeoutFake,
+            clearTimeout: sinon.fake(),
+        };
+        const clock = FakeTimers.withGlobal(context).install();
+
+        clock.uninstall();
+        globalClock.uninstall();
+    });
+
+    it("should allow a fake on the global if a fake on a customer target is already defined", () => {
+        const setTimeoutFake = sinon.fake();
+        const context = {
+            Date: Date,
+            setTimeout: setTimeoutFake,
+            clearTimeout: sinon.fake(),
+        };
+        const clock = FakeTimers.withGlobal(context).install();
+        const globalClock = FakeTimers.install();
+
+        globalClock.uninstall();
+        clock.uninstall();
+    });
+});
 describe("issue #59", function () {
     it("should install and uninstall the clock on a custom target", function () {
         const setTimeoutFake = sinon.fake();