Bug 1520018: Add web-platform-test for table element's UA-stylesheet-provided CSS rules. r=heycam

Differential Revision: https://phabricator.services.mozilla.com/D20892 --HG-- extra : moz-landing-system : lando
2019-02-26 19:29:58 +00:00 · 2019-02-26 19:29:58 +00:00 · 330206c35c
--- a/testing/web-platform/tests/html/rendering/non-replaced-elements/tables/table-ua-stylesheet.html
+++ b/testing/web-platform/tests/html/rendering/non-replaced-elements/tables/table-ua-stylesheet.html
@ -0,0 +1,44 @@
+<!DOCTYPE html>
+<meta charset="utf-8">
+<title>Test for table element's UA-stylesheet-provided styles</title>
+<link rel="help" href="https://html.spec.whatwg.org/multipage/rendering.html#the-css-user-agent-style-sheet-and-presentational-hints">
+<link rel="help" href="https://html.spec.whatwg.org/multipage/rendering.html#tables-2">
+<link rel="author" title="Daniel Holbert" href="mailto:dholbert@mozilla.com">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+
+<div id="refElem"></div>
+<!-- Note: this test puts the table inside of an element with a non-default
+     'text-indent' and 'border-collapse' values, so that we can verify that
+     the table does indeed use the initial value for these properties, rather
+     than simply inheriting. -->
+<div style="text-indent: 100px; border-collapse: collapse">
+  <table id="tableElem"></table>
+</div>
+
+<script>
+/* These styles come from the default `table` styling here:
+ *  https://html.spec.whatwg.org/multipage/rendering.html#tables-2
+ * We can't check for these values directly, because they may be
+ * serialized slightly differently when read from the computed style.
+ * So, for each property here, we apply it to a "reference" div and then
+ * read back the computed value, and we validate that a table element
+ * has that same computed value by default. */
+const defaultTablePropVals = {
+  'display':         'table',
+  'box-sizing':      'border-box',
+  'border-spacing':  '2px',
+  'border-collapse': 'separate',
+  'text-indent':     'initial',
+};
+
+for (var propName in defaultTablePropVals) {
+  test(function() {
+    refElem.style[propName] = defaultTablePropVals[propName];
+    let expectedComputedVal = getComputedStyle(refElem, "")[propName];
+
+    let actualComputedVal = getComputedStyle(tableElem, "")[propName];
+    assert_equals(actualComputedVal, expectedComputedVal);
+  }, `Computed '${propName}' on table should match html spec`);
+}
+</script>