{"id":127,"date":"2015-12-10T09:26:09","date_gmt":"2015-12-10T16:26:09","guid":{"rendered":"http:\/\/blog.mozilla.org\/mrbkap\/?p=127"},"modified":"2015-12-10T09:26:09","modified_gmt":"2015-12-10T16:26:09","slug":"converting-a-test-to-be-e10s-compatible","status":"publish","type":"post","link":"https:\/\/blog.mozilla.org\/mrbkap\/2015\/12\/10\/converting-a-test-to-be-e10s-compatible\/","title":{"rendered":"Converting a test to be e10s compatible"},"content":{"rendered":"

I was working on another bug the other day when I came across a disabled test<\/a>. The comment for why it was disabled seemed like it might be low-hanging fruit for conversion to be e10s<\/code>-compatible, so I took a look.<\/a> <\/p>\n

A couple of things leapt out to me immediately: the test isn’t using BrowserTestUtils<\/code><\/a> and it isn’t using promises. So, the first step is to convert it to use BrowserTestUtils<\/code> and Promise<\/code>. Here’s the diff.<\/a><\/p>\n

Now that we’re using promises and the nice helpers, let’s see why the test isn’t compatible. The first load<\/a> is of a chrome:\/\/<\/code> URL. This is guaranteed to load in the parent, meaning that our first test, testXFOFrameInChrome<\/code> can remain untouched. We can use its contentWindow<\/code> with impunity.<\/p>\n

The second test, testXFOFrameInContent<\/code> is the reason this blog post exists. It loads a content document, meaning that its browser will be a remote browser and the contentWindow<\/code> would be a CPOW.<\/a> Instead of using it directly, we can use another helper: ContentTask<\/code>.<\/a> This will let us perform an operation in a given browser<\/code>‘s associated child process and fulfill a Promise<\/code> when it finishes. Here’s that change<\/a>.<\/p>\n

We’re almost done! However, if we run this version, we’ll still fail due to a small difference between the function is<\/code> in browser-chrome tests and in ContentTask.jsm<\/code>. The version in ContentTask.jsm<\/code> is stricter than that of the normal tests, so when we check the return value of document.getElementById<\/code> against undefined<\/code> we get a test failure. We fix that by checking against the correct value<\/a> (null<\/code>). Another thing to note is that ContentTask<\/code> decompiles and recompiles the callback function in the child process. That means that you can’t use any global variables or functions. You can pass a single parameter to the function, though, as long as it can be structured cloned. The content window is available through the content<\/code> global in frame scripts.<\/p>\n

One last note about this test. When I was writing it, I used BrowserTestUtils.loadURI<\/code> function which returns a Promise<\/code>. However, that promise doesn’t resolve when the URI is loaded, only when the load starts. So I ended up wasting a bunch of time before realizing that I needed to use BrowserTestUtils.browserLoaded<\/code> after it to ensure the second test runs at the right time.<\/p>\n

Now, our test passes and we can get it reviewed and checked in!<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"

I was working on another bug the other day when I came across a disabled test. The comment for why it was disabled seemed like it might be low-hanging fruit for conversion to be e10s-compatible, so I took a look. A couple of things leapt out to me immediately: the test isn’t using BrowserTestUtils and […]<\/p>\n","protected":false},"author":149,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[],"_links":{"self":[{"href":"https:\/\/blog.mozilla.org\/mrbkap\/wp-json\/wp\/v2\/posts\/127"}],"collection":[{"href":"https:\/\/blog.mozilla.org\/mrbkap\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blog.mozilla.org\/mrbkap\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blog.mozilla.org\/mrbkap\/wp-json\/wp\/v2\/users\/149"}],"replies":[{"embeddable":true,"href":"https:\/\/blog.mozilla.org\/mrbkap\/wp-json\/wp\/v2\/comments?post=127"}],"version-history":[{"count":0,"href":"https:\/\/blog.mozilla.org\/mrbkap\/wp-json\/wp\/v2\/posts\/127\/revisions"}],"wp:attachment":[{"href":"https:\/\/blog.mozilla.org\/mrbkap\/wp-json\/wp\/v2\/media?parent=127"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blog.mozilla.org\/mrbkap\/wp-json\/wp\/v2\/categories?post=127"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blog.mozilla.org\/mrbkap\/wp-json\/wp\/v2\/tags?post=127"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}