Add countTimers method

Readme.md

@@ -200,6 +200,11 @@ available in both browser & node environments.
 
 Cancels the callback scheduled by the provided id.
 
+### `clock.countTimers()`
+
+Returns the number of waiting timers. This can be used to assert that a test
+finishes without leaking any timers.
+
 ### `clock.hrtime(prevTime?)`
 Only available in Node.js, mimicks process.hrtime().
 

src/lolex-src.js

@@ -257,7 +257,6 @@ function withGlobal(_global) {
         return timer.id;
     }
 
-
     /* eslint consistent-return: "off" */
     function compareTimers(a, b) {
         // Sort first by absolute timing
@@ -574,6 +573,10 @@ function withGlobal(_global) {
             return clearTimer(clock, timerId, "Immediate");
         };
 
+        clock.countTimers = function countTimers() {
+            return Object.keys(clock.timers || {}).length;
+        };
+
         clock.requestAnimationFrame = function requestAnimationFrame(func) {
             var result = addTimer(clock, {
                 func: func,

test/lolex-test.js

@@ -432,6 +432,26 @@ describe("lolex", function () {
 
     });
 
+    describe("countTimers", function () {
+
+        beforeEach(function () {
+            this.clock = lolex.createClock();
+        });
+
+        it("return zero for a fresh clock", function () {
+            assert.equals(this.clock.countTimers(), 0);
+        });
+
+        it("counts remaining timers", function () {
+            this.clock.setTimeout(NOOP, 100);
+            this.clock.setTimeout(NOOP, 200);
+            this.clock.setTimeout(NOOP, 300);
+            this.clock.tick(150);
+            assert.equals(this.clock.countTimers(), 2);
+        });
+
+    });
+
     describe("tick", function () {
 
         beforeEach(function () {