Start using /list_tests to populate subtest menus in test-picker

dashboard/dashboard/elements/test-picker-test.html

Index: dashboard/dashboard/elements/test-picker-test.html
diff --git a/dashboard/dashboard/elements/test-picker-test.html b/dashboard/dashboard/elements/test-picker-test.html
index bcfc477f91138a5440a03c2c4d1c1bfbecfee25d..141fb9c9557ed24ef65fff05a5ac2fc657a486ce 100644
--- a/dashboard/dashboard/elements/test-picker-test.html
+++ b/dashboard/dashboard/elements/test-picker-test.html
@@ -110,7 +110,6 @@ tr.b.unittest.testSuite(function() {
   }, testOptions);
 
   test('fullPathRetained', function() {
-    testing_common.addXhrMock('*', JSON.stringify(MOCK_RESPONSE));
     let testPicker = document.createElement('test-picker');
     testPicker.testSuites = {
       'endure': {
@@ -125,12 +124,18 @@ tr.b.unittest.testSuite(function() {
         'mon': ['select-multiple-add/select-multiple-add.html']
       }
     };
+    testPicker.subtests.prepopulate({
+      'Chromium/mac/blink_perf': ['Chromium/mac/blink_perf/textarea-edit'],
+      'Chromium/mac/blink_perf/textarea-edit': [
+        'Chromium/mac/blink_perf/textarea_edit.html']
+    });
 
     let suiteMenu = testPicker.getSelectionMenu(0);
     suiteMenu.selectedItem = suiteMenu.items[0];
 
     let botMenu = testPicker.getSelectionMenu(1);
-    botMenu.selectedItem = botMenu.items[0];
+    // Pick the second bot menu item because the first is the master.
+    botMenu.selectedItem = botMenu.items[1];

[eakuefner, 2017/04/13 23:26:03]

The problem with this is, mutating selectedItem like this causes Polymer to call
onDropdownSelect which then calls updateSubtestMenus, which is asynchronous and
causes the benchmark menu to be populated. Hence, below when we say let
benchmarkMenu = testPicker.getSelectionMenu(2), it doesn't return the would-be
second menu. Previously, this didn't matter, because the XHR mocks worked
synchronously.

I'm not sure what the best way to do this, because we don't have access to the
promise returned by updateSubtestMenus so we can't await it. We could call
updateSubtestMenus explicitly here, in which case we would duplicate effort but
be able to explicitly await that call, but I'm also wondering if this is a
discussion we should punt, at the cost of this bit of test coverage.

[sullivan, 2017/04/14 00:37:30]

2 things:

1) I think it's okay to expicitly call updateSubtestMenus in order to keep this
test passing, because this is a feature that has broken in the past.
2) Since you re-implemented to have a memoization pattern, shouldn't there be a
simple test that uses it as intended?

[eakuefner, 2017/04/14 17:34:26]

Done.
Added a test that uses an XHR mock to test fetching behavior, a test that tests
prepopulate, and finally a smoke test that ensures that Subtests stores
promises.

 
     let benchmarkMenu = testPicker.getSelectionMenu(2);
     let expectedBenchmark = benchmarkMenu.items[0].name;
@@ -147,8 +152,7 @@ tr.b.unittest.testSuite(function() {
     assert.deepEqual(metricMenu.selectedItem.name, expectedMetric);
   }, testOptions);
 
-  test('getCurrentSelectionReturnsNullIfInvalid', async function() {
-    testing_common.addXhrMock('*', JSON.stringify(MOCK_RESPONSE));
+  test('getCurrentSelectionReturnsUndefinedIfInvalid', async function() {
     let testPicker = document.createElement('test-picker');
     testPicker.testSuites = {
       'endure': {
@@ -170,8 +174,7 @@ tr.b.unittest.testSuite(function() {
     let botMenu = testPicker.getSelectionMenu(1);
     botMenu.selectedItem = botMenu.items[0];
 
-    assert.isNull(await testPicker.getCurrentSelection());
-    testing_common.clearXhrMock();
+    assert.isUndefined(await testPicker.getCurrentSelection());
   });
 });
 </script>