Merge pull request discourse#1489 from velesin/debounce_tests

adds unit tests for Discourse.debounce

Author: eviltrout

test/javascripts/components/debounce_test.js

@@ -0,0 +1,86 @@
+var clock, original, debounced;
+
+var firedOnce = function(message) {
+  ok(original.calledOnce, message);
+};
+
+var notFired = function(message) {
+  ok(!original.called, message);
+};
+
+module("Discourse.debounce", {
+  setup: function() {
+    clock = sinon.useFakeTimers();
+    original = sinon.spy();
+    debounced = Discourse.debounce(original, 100);
+  },
+
+  teardown: function() {
+    clock.restore();
+  }
+});
+
+test("delays function execution till the end of the timeout", function() {
+  debounced();
+  notFired("immediately after calling debounced function nothing happens");
+
+  clock.tick(99);
+  notFired("just before the end of the timeout still nothing happens");
+
+  clock.tick(1);
+  firedOnce("exactly at the end of the timeout the function is executed");
+});
+
+test("executes delayed function only once, no matter how many times debounced function is called during the timeout", function() {
+  debounced();
+  debounced();
+
+  clock.tick(100);
+  firedOnce("second call was supressed");
+});
+
+test("does not prolong the timeout when the debounced function is called for the second time during the timeout", function() {
+  debounced();
+
+  clock.tick(50);
+  debounced();
+
+  clock.tick(50);
+  firedOnce("function is executed exactly at the end of the original timeout");
+});
+
+test("returns a JS timer handle that allows delayed execution to be cancelled before the timeout ends", function() {
+  var timerId = debounced();
+
+  clock.tick(50);
+  clearTimeout(timerId);
+
+  clock.tick(50);
+  notFired("timeout has ended but function was not executed");
+});
+
+test("preserves first call's context and params when executing delayed function", function() {
+  var firstObj = {};
+  var secondObj = {};
+
+  debounced.call(firstObj, "first");
+  debounced.call(secondObj, "second");
+
+  clock.tick(100);
+  ok(original.calledOn(firstObj), "the context of the first of two subsequent calls is preserved");
+  ok(original.calledWithExactly("first"), "param passed during the first of two subsequent calls is preserved");
+});
+
+test("can be called again (with a different context and params) after timeout passes", function() {
+  var firstObj = {};
+  var secondObj = {};
+
+  debounced.call(firstObj, "first");
+
+  clock.tick(100);
+  debounced.call(secondObj, "second");
+
+  clock.tick(100);
+  ok(original.calledOn(secondObj), "function is executed with the context of the call made after the timeout has passed");
+  ok(original.calledWithExactly("second"), "function is executed with the param passed to the call made after the timeout has passed");
+});