зеркало из https://github.com/mozilla/pjs.git
261 строка
11 KiB
Plaintext
261 строка
11 KiB
Plaintext
Layout Engine Visual Tests (reftest)
|
|
L. David Baron <dbaron@dbaron.org>, Mozilla Corporation
|
|
July 19, 2006
|
|
|
|
This code is designed to run tests of Mozilla's layout engine. These
|
|
tests consist of an HTML (or other format) file along with a reference
|
|
in the same format. The tests are run based on a manifest file, and for
|
|
each test, PASS or FAIL is reported, and UNEXPECTED is reported if the
|
|
result (PASS or FAIL) was not the expected result noted in the manifest.
|
|
|
|
Why this way?
|
|
=============
|
|
|
|
Writing HTML tests where the reference rendering is also in HTML is
|
|
harder than simply writing bits of HTML that can be regression-tested by
|
|
comparing the rendering of an older build to that of a newer build
|
|
(perhaps using stored reference images from the older build). However,
|
|
comparing across time has major disadvantages:
|
|
|
|
* Comparisons across time either require two runs for every test, or
|
|
they require stored reference images appropriate for the platform and
|
|
configuration (often limiting testing to a very specific
|
|
configuration).
|
|
|
|
* Comparisons across time may fail due to expected changes, for
|
|
example, changes in the default style sheet for HTML, changes in the
|
|
appearance of form controls, or changes in default preferences like
|
|
default font size or default colors.
|
|
|
|
Using tests for which the pass criteria were explicitly chosen allows
|
|
running tests at any time to see whether they still pass.
|
|
|
|
Manifest Format
|
|
===============
|
|
|
|
The test manifest format is a plain text file. A line starting with a
|
|
"#" is a comment. Lines may be commented using whitespace followed by
|
|
a "#" and the comment. Each non-blank line (after removal of comments)
|
|
must be one of the following:
|
|
|
|
1. Inclusion of another manifest
|
|
|
|
include <relative_path>
|
|
|
|
2. A test item
|
|
|
|
<failure-type>* [<http>] <type> <url> <url_ref>
|
|
|
|
where
|
|
|
|
a. <failure-type> (optional) is one of the following:
|
|
|
|
fails The test passes if the images of the two renderings DO NOT
|
|
meet the conditions specified in the <type>.
|
|
|
|
fails-if(condition) If the condition is met, the test passes if the
|
|
images of the two renderings DO NOT meet the
|
|
conditions of <type>. If the condition is not met,
|
|
the test passes if the conditions of <type> are met.
|
|
|
|
random The results of the test are random and therefore not to be
|
|
considered in the output.
|
|
|
|
random-if(condition) The results of the test are random if a given
|
|
condition is met.
|
|
|
|
skip This test should not be run. This is useful when a test fails in a
|
|
catastrophic way, such as crashing or hanging the browser. Using
|
|
'skip' is preferred to simply commenting out the test because we
|
|
want to report the test failure at the end of the test run.
|
|
|
|
skip-if(condition) If the condition is met, the test is not run. This is
|
|
useful if, for example, the test crashes only on a
|
|
particular platform (i.e. it allows us to get test
|
|
coverage on the other platforms).
|
|
|
|
Examples of using conditions:
|
|
fails-if(MOZ_WIDGET_TOOLKIT=="windows") ...
|
|
fails-if(MOZ_WIDGET_TOOLKIT=="cocoa") ...
|
|
fails-if(MOZ_WIDGET_TOOLKIT=="gtk2") ...
|
|
|
|
b. <http>, if present, is the string "HTTP" (sans quotes), indicating that
|
|
the test should be run over an HTTP server because it requires certain
|
|
HTTP headers or a particular HTTP status. (Don't use this if your test
|
|
doesn't require this functionality, because it unnecessarily slows down
|
|
the test.)
|
|
|
|
HTTP tests have the restriction that any resource an HTTP test accesses
|
|
must be accessed using a relative URL, and the test and the resource must
|
|
be within the directory containing the reftest manifest that describes
|
|
the test (or within a descendant directory).
|
|
|
|
To modify the HTTP status or headers of a resource named FOO, create a
|
|
sibling file named FOO^headers^ with the following contents:
|
|
|
|
[<http-status>]
|
|
<http-header>*
|
|
|
|
<http-status> A line of the form "HTTP ###[ <description>]", where
|
|
### indicates the desired HTTP status and <description>
|
|
indicates a desired HTTP status description, if any.
|
|
If this line is omitted, the default is "HTTP 200 OK".
|
|
<http-header> A line in standard HTTP header line format, i.e.
|
|
"Field-Name: field-value". You may not repeat the use
|
|
of a Field-Name and must coalesce such headers together,
|
|
and each header must be specified on a single line, but
|
|
otherwise the format exactly matches that from HTTP
|
|
itself.
|
|
|
|
c. <type> is one of the following:
|
|
|
|
== The test passes if the images of the two renderings are the
|
|
SAME.
|
|
!= The test passes if the images of the two renderings are
|
|
DIFFERENT.
|
|
load The test passes unconditionally if the page loads. url_ref
|
|
must be omitted, and the test cannot be marked as fails or
|
|
random. (Used to test for crashes, hangs, assertions, and
|
|
leaks.)
|
|
|
|
d. <url> is either a relative file path or an absolute URL for the
|
|
test page
|
|
|
|
e. <url_ref> is either a relative file path or an absolute URL for
|
|
the reference page
|
|
|
|
The only difference between <url> and <url_ref> is that results of
|
|
the test are reported using <url> only.
|
|
|
|
This test manifest format could be used by other harnesses, such as ones
|
|
that do not depend on XUL, or even ones testing other layout engines.
|
|
|
|
Running Tests
|
|
=============
|
|
|
|
At some point in the future there will hopefully be a cleaner way to do
|
|
this. For now, go to your object directory, and run (perhaps using
|
|
MOZ_NO_REMOTE=1 or the -profile <directory> option)
|
|
|
|
./firefox -reftest /path/to/srcdir/mozilla/layout/reftests/reftest.list > reftest.out
|
|
|
|
and then search/grep reftest.out for "UNEXPECTED".
|
|
|
|
There are two scripts provided to convert the reftest.out to HTML.
|
|
clean-reftest-output.pl converts reftest.out into simple HTML, stripping
|
|
lines from the log that aren't relevant. reftest-to-html.pl converts
|
|
the output into html that makes it easier to visually check for
|
|
failures.
|
|
|
|
Testable Areas
|
|
==============
|
|
|
|
This framework is capable of testing many areas of the layout engine.
|
|
It is particularly well-suited to testing dynamic change handling (by
|
|
comparison to the static end-result as a reference) and incremental
|
|
layout (comparison of a script-interrupted layout to one that was not).
|
|
However, it is also possible to write tests for many other things that
|
|
can be described in terms of equivalence, for example:
|
|
|
|
* CSS cascading could be tested by comparing the result of a
|
|
complicated set of style rules that makes a word green to <span
|
|
style="color:green">word</span>.
|
|
|
|
* <canvas> compositing operators could be tested by comparing the
|
|
result of drawing using canvas to a block-level element with the
|
|
desired color as a CSS background-color.
|
|
|
|
* CSS counters could be tested by comparing the text output by counters
|
|
with a page containing the text written out
|
|
|
|
* complex margin collapsing could be tested by comparing the complex
|
|
case to a case where the margin is written out, or where the margin
|
|
space is created by an element with 'height' and transparent
|
|
background
|
|
|
|
When it is not possible to test by equivalence, it may be possible to
|
|
test by non-equivalence. For example, testing justification in cases
|
|
with more than two words, or more than three different words, is
|
|
difficult. However, it is simple to test that justified text is at
|
|
least displayed differently from left-, center-, or right-aligned text.
|
|
|
|
Writing Tests
|
|
=============
|
|
|
|
When writing tests for this framework, it is important for the test to
|
|
depend only on behaviors that are known to be correct and permanent.
|
|
For example, tests should not depend on default font sizes, default
|
|
margins of the body element, the default style sheet used for HTML, the
|
|
default appearance of form controls, or anything else that can be
|
|
avoided.
|
|
|
|
In general, the best way to achieve this is to make the test and the
|
|
reference identical in as many aspects as possible. For example:
|
|
|
|
Good test markup:
|
|
<div style="color:green"><table><tr><td><span>green
|
|
</span></td></tr></table></div>
|
|
|
|
Good reference markup:
|
|
<div><table><tr><td><span style="color:green">green
|
|
</span></td></tr></table></div>
|
|
|
|
BAD reference markup:
|
|
<!-- 3px matches the default cellspacing and cellpadding -->
|
|
<div style="color:green; padding: 3px">green
|
|
</div>
|
|
|
|
BAD test markup:
|
|
<!-- span doesn't change the positioning, so skip it -->
|
|
<div style="color:green"><table><tr><td>green
|
|
</td></tr></table></div>
|
|
|
|
Asynchronous Tests
|
|
==================
|
|
|
|
Normally reftest takes a snapshot of the given markup's rendering right
|
|
after the load event fires for content. If your test needs to postpone
|
|
the moment the snapshot is taken, it should make sure a class
|
|
'reftest-wait' is on the root element by the moment the load event
|
|
fires. The easiest way to do this is to put it in the markup, e.g.:
|
|
<html class="reftest-wait">
|
|
|
|
When your test is ready, you should remove this class from the root
|
|
element, for example using this code:
|
|
document.documentElement.className = "";
|
|
|
|
|
|
Note that in layout tests it is often enough to trigger layout using
|
|
document.body.offsetWidth // HTML example
|
|
|
|
When possible, you should use this technique instead of making your
|
|
test async.
|
|
|
|
Printing Tests
|
|
==============
|
|
Now that the patch for bug 374050 has landed
|
|
(https://bugzilla.mozilla.org/show_bug.cgi?id=374050), it is possible to
|
|
create reftests that run in a paginated context.
|
|
|
|
The page size used is 5in wide and 3in tall (with the default half-inch
|
|
margins). This is to allow tests to have less text and to make the
|
|
entire test fit on the screen.
|
|
|
|
There is a layout/reftests/printing directory for printing reftests; however,
|
|
there is nothing special about this directory. You can put printing reftests
|
|
anywhere that is appropriate.
|
|
|
|
The suggested first lines for any printing test is
|
|
<!DOCTYPE html><html class="reftest-print">
|
|
<style>html{font-size:12pt}</style>
|
|
|
|
The reftest-print class on the root element triggers the reftest to
|
|
switch into page mode on load. Fixing the font size is suggested,
|
|
although not required, because the pages are a fixed size in inches.
|
|
|
|
The underlying layout support for this mode isn't really complete; it
|
|
doesn't use exactly the same codepath as real print preview/print. In
|
|
particular, scripting and frames are likely to cause problems; it is untested,
|
|
though. That said, it should be sufficient for testing layout issues related
|
|
to pagination.
|