1 files changed, 60 insertions, 0 deletions
diff --git a/testing/web-platform/tests/common/subset-tests.js b/testing/web-platform/tests/common/subset-tests.js
new file mode 100644
index 0000000000..58e93413de
--- /dev/null
+++ b/testing/web-platform/tests/common/subset-tests.js
@@ -0,0 +1,60 @@
+(function() {
+  var subTestStart = 0;
+  var subTestEnd = Infinity;
+  var match;
+  if (location.search) {
+    match = /(?:^\?|&)(\d+)-(\d+|last)(?:&|$)/.exec(location.search);
+    if (match) {
+      subTestStart = parseInt(match[1], 10);
+      if (match[2] !== "last") {
+          subTestEnd = parseInt(match[2], 10);
+      }
+    }
+    // Below is utility code to generate <meta> for copy/paste into tests.
+    // Sample usage:
+    // test.html?split=1000
+    match = /(?:^\?|&)split=(\d+)(?:&|$)/.exec(location.search);
+    if (match) {
+      var testsPerVariant = parseInt(match[1], 10);
+      add_completion_callback(tests => {
+        var total = tests.length;
+        var template = '<meta name="variant" content="?%s-%s">';
+        var metas = [];
+        for (var i = 1; i < total - testsPerVariant; i = i + testsPerVariant) {
+          metas.push(template.replace("%s", i).replace("%s", i + testsPerVariant - 1));
+        }
+        metas.push(template.replace("%s", i).replace("%s", "last"));
+        var pre = document.createElement('pre');
+        pre.textContent = metas.join('\n');
+        document.body.insertBefore(pre, document.body.firstChild);
+        document.getSelection().selectAllChildren(pre);
+      });
+    }
+  }
+  /**
+   * Check if `currentSubTest` is in the subset specified in the URL.
+   * @param {number} currentSubTest
+   * @returns {boolean}
+   */
+  function shouldRunSubTest(currentSubTest) {
+    return currentSubTest >= subTestStart && currentSubTest <= subTestEnd;
+  }
+  var currentSubTest = 0;
+  /**
+   * Only test a subset of tests with, e.g., `?1-10` in the URL.
+   * Can be used together with `<meta name="variant" content="...">`
+   * Sample usage:
+   * for (const test of tests) {
+   *   subsetTest(async_test, test.fn, test.name);
+   * }
+   */
+  function subsetTest(testFunc, ...args) {
+    currentSubTest++;
+    if (shouldRunSubTest(currentSubTest)) {
+      return testFunc(...args);
+    }
+    return null;
+  }
+  self.shouldRunSubTest = shouldRunSubTest;
+  self.subsetTest = subsetTest;
+})();