Make Cache Storage tests resilient to execution order

third_party/WebKit/LayoutTests/http/tests/cachestorage/script-tests/cache-storage.js

 if (self.importScripts) {
     importScripts('/resources/testharness.js');
     importScripts('../resources/test-helpers.js');
 }
 
 promise_test(function(t) {
     var cache_name = 'cache-storage/foo';
     return self.caches.delete(cache_name)
       .then(function() {
           return self.caches.open(cache_name);
@@ skipping 185 matching lines @@
 promise_test(function(t) {
     return self.caches.delete('cheezburger')
       .then(function(result) {
           assert_false(result,
                        'CacheStorage.delete should return false for a ' +
                        'nonexistent cache.');
         });
   }, 'CacheStorage.delete with nonexistent cache');
 
 promise_test(function(t) {
-    var bad_name = 'unpaired\uD800';
-    var converted_name = 'unpaired\uFFFD'; // Don't create cache with this name.
-    return self.caches.has(converted_name)
+    var unpaired_name = 'unpaired\uD800';
+    var converted_name = 'unpaired\uFFFD';
+
+    // The test assumes that a cache with converted_name does not
+    // exist, but if the implementation fails the test then such
+    // a cache will be created. Start off in a fresh state by
+    // deleting all caches.
+    return delete_all_caches()

[jkarlin, 2016/11/22 18:20:40]

Why not have promise_test run delete_all_caches at the end instead of having to
insert it into tests?

[jsbell, 2016/11/22 18:34:14]

promise_test is generic (part of testharness.js); we could rework all of these
test to go through a common wrapper, but I'd rather do that upstream.

+      .then(function() {
+          return self.caches.has(converted_name);
+      })
       .then(function(cache_exists) {
           assert_false(cache_exists,
                        'Test setup failure: cache should not exist');
       })
-      .then(function() { return self.caches.open(bad_name); })
+      .then(function() { return self.caches.open(unpaired_name); })
       .then(function() { return self.caches.keys(); })
       .then(function(keys) {
-          assert_true(keys.indexOf(bad_name) !== -1,
+          assert_true(keys.indexOf(unpaired_name) !== -1,
                       'keys should include cache with bad name');
       })
-      .then(function() { return self.caches.has(bad_name); })
+      .then(function() { return self.caches.has(unpaired_name); })
       .then(function(cache_exists) {
           assert_true(cache_exists,
                       'CacheStorage names should be not be converted.');
         })
       .then(function() { return self.caches.has(converted_name); })
       .then(function(cache_exists) {
           assert_false(cache_exists,
                        'CacheStorage names should be not be converted.');
         });
   }, 'CacheStorage names are DOMStrings not USVStrings');
 
 done();