Import wpt@ed94c51f3dfaa5ff4c9c311add1a560408059c51

third_party/WebKit/LayoutTests/imported/wpt/web-animations/README.md

-Web Animations Tests
-====================
+Web Animations Test Suite
+=========================
 
-Specification: http://w3c.github.io/web-animations/
+Specification: https://w3c.github.io/web-animations/
+
+
+Guidelines for writing tests
+----------------------------
+
+*   Try to follow the spec outline where possible.
+
+    For example, if you want to test setting the start time, you might be
+    tempted to put all the tests in:
+
+    > `/web-animations/Animation/startTime.html`
+
+    However, in the spec most of the logic is in the “Set the animation
+    start time“ procedure in the “Timing model” section.
+
+    Instead, try something like:
+
+    > *   `/web-animations/timing-model/animation/set-the-animation-start-time.html`<br>
+    >     Tests all the branches and inputs to the procedure as defined in the
+    >     spec (using the `Animation.startTime` API).
+    > *   `/web-animations/Animation/startTime.html`<br>
+    >     Tests API-layer specific issues like mapping unresolved values to
+    >      null, etc.
+
+    On that note, two levels of subdirectories is enough even if the spec has
+    deeper nesting.
+
+    Note that most of the existing tests in the suite _don't_ do this well yet.
+    That's the direction we're heading, however.
+
+*   Test the spec.
+
+    *   If the spec defines a timing calculation that is directly
+        reflected in the iteration progress
+        (i.e. `anim.effect.getComputedTiming().progress`), test that instead
+        of calling `getComputedStyle(elem).marginLeft`.
+
+    *   Likewise, don't add needless tests for `anim.playbackState`.
+        The playback state is a calculated value based on other values.
+        It's rarely necessary to test directly unless you need, for example,
+        to check that a pending task is scheduled (which isn't observable
+        elsewhere other than waiting for the corresponding promise to
+        complete).
+
+*   Try to keep tests as simple and focused as possible.
+
+    e.g.
+
+    ```javascript
+  test(function(t) {
+    var anim = createDiv(t).animate(null);
+    assert_class_string(anim, 'Animation', 'Returned object is an Animation');
+  }, 'Element.animate() creates an Animation object');
+    ```
+
+    ```javascript
+  test(function(t) {
+    assert_throws({ name: 'TypeError' }, function() {
+      createDiv(t).animate(null, -1);
+    });
+  }, 'Setting a negative duration throws a TypeError');
+    ```
+
+    ```javascript
+  promise_test(function(t) {
+    var animation = createDiv(t).animate(null, 100 * MS_PER_SEC);
+    return animation.ready.then(function() {
+      assert_greater_than(animation.startTime, 0, 'startTime when running');
+    });
+  }, 'startTime is resolved when running');
+    ```
+
+    If you're generating complex test loops and factoring out utility functions
+    that affect the logic of the test (other than, say, simple assertion utility
+    functions), you're probably doing it wrong.
+
+    It should be possible to understand exactly what the test is doing at a
+    glance without having to scroll up and down the test file and refer to
+    other files.
+
+    See Justin Searls' presentation, [&ldquo;How to stop hating your
+    tests&rdquo;](http://blog.testdouble.com/posts/2015-11-16-how-to-stop-hating-your-tests.html)
+    for some tips on making your tests simpler.
+
+*   Assume tests will run on under-performing hardware where the time between
+    animation frames might run into 10s of seconds.
+    As a result, animations that are expected to still be running during
+    the test should be at least 100s in length.
+
+*   Avoid using `GLOBAL_CONSTS` that make the test harder to read.
+    It's fine to repeat the the same parameter values like `100 * MS_PER_SEC`
+    over and over again since it makes it easy to read and debug a test in
+    isolation.
+    Remember, even if we do need to make all tests take, say 200s each, text
+    editors are very good at search and replace.
+
+*   Use the `assert_times_equal` assertion for comparing calculated times.
+    It tests times are equal using the precision recommended in the spec whilst
+    allowing implementations to override the function to meet their own
+    precision requirements.
+
+*   There are quite a few bad tests in the repository. We're learning as
+    we go. Don't just copy them blindly&mdash;please fix them!