This document offers some basic tips for writing Mochitest tests. (See also this Mochitest page on MDN, which is Firefox-centric but may still be useful.)
Adding a New Test
You may be writing a new test in an existing test file, or you may have set up a new test file as described in Adding Tests. Either way, add a new test with the add_task function:
This document is a basic introduction. To go further, explore these files (particularly the docstrings of the various functions in them) and look at existing tests.
Assertion Functions
Use the is and ok functions to make test assertions. is compares two values (using JavaScript's === equality comparison). ok asserts that a single value is truthy (in JavaScript's sense of truthy).
The last argument to each is a message printed to the console to identify the assertion. It is optional but is a good practice for more understandable test logs.
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let sum =3*4;
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is(sum,12,"multiplication appears to still be working");
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​
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let truthy =true;
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ok(truthy,"thing is not falsy");
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Mouse Clicks
Do a single click on a DOM element:
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let element = document.getElementById("some-element-id");
To press a key along with one or more modifier keys:
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// Ctrl+A:
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EventUtils.synthesizeKey("a",{ accelKey:true});
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​
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// Ctrl+Alt+B (no shift key):
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EventUtils.synthesizeKey("b",{
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accelKey:true,
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altKey:true,
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shiftKey:false
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});
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Some other options are altKey, shiftKey, and ctrlKey (a non-exhaustive list).
Similar to sendString and sendKey, there is an optional third window argument to use when interacting with a specific window.
Waiting for Events
Tests move faster than users. Sometimes too fast. The test may need to wait for an event to occur before doing the next thing.
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let element = document.getElementById("some-element-id");
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​
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let event =await BrowserTestUtils.waitForEvent(element,"focus");
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​
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is(event.type,"focus","element is focused");
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Letting Thunderbird Respond Before Proceeding
Sometimes the test needs to let the application respond to something the test did before moving on to the next step, and there is not an event to listen for. Here is a simple way to do this:
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// Do something here involving the UI.
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​
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// Let the application finish responding to what the test just did.
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awaitnewPromise(resolve=>setTimeout(resolve));
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​
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// Do the next thing.
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Interacting with Regular Windows
Some tests will need to interact with windows that are not the main window. For exaple, below is a function that opens the address book window. It returns the window (nsIDOMWindow) object for the address book window, which can then be used when calling functions like EventUtils.sendKey.
The key point is the use of BrowserTestUtils.domWindowOpened, but this example also demonstrates some of the other tips found in this document. (See below for dialog windows which are handled differently.)
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asyncfunctionopenAddressBookWindow(){
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// Set up a watcher for "domwindowopened". When DOM windows are opened the
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// function supplied as a second argument is called. When it returns true the
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// promise is resolved as the nsIDOMWindow object for the window.
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let addressBookWindowPromise = BrowserTestUtils.domWindowOpened(
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null,
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asyncwin=>{
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// win is the nsIDOMWindow object for a window that is opening.
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​
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// Wait until the "load" event has happened for the window.