Do not complain about empty auto-index file

AppEngineRule throws an exception during teardown if
an empty datastore-indexes-auto.xml is created during
testing. This scenario should be fine, just like if this file
has not been created at all.

This issue causes some flakiness in tests.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=231229692

javatests/google/registry/testing/AppEngineRule.java

@@ -94,7 +94,7 @@ public final class AppEngineRule extends ExternalResource {
   private LocalServiceTestHelper helper;
 
   /** A rule-within-a-rule to provide a temporary folder for AppEngineRule's internal temp files. */
-  private TemporaryFolder temporaryFolder = new TemporaryFolder();
+  TemporaryFolder temporaryFolder = new TemporaryFolder();
 
   private boolean withDatastore;
   private boolean withLocalModules;
@@ -328,14 +328,22 @@ public final class AppEngineRule extends ExternalResource {
     helper.tearDown();
     helper = null;
     // Test that Datastore didn't need any indexes we don't have listed in our index file.
+    File indexFile = new File(temporaryFolder.getRoot(), "datastore-indexes-auto.xml");
+    if (!indexFile.exists()) {
+      return;
+    }
     try {
-      Set<String> autoIndexes = getIndexXmlStrings(Files.asCharSource(
+      String indexFileContent = Files.asCharSource(indexFile, UTF_8).read();
-          new File(temporaryFolder.getRoot(), "datastore-indexes-auto.xml"), UTF_8).read());
+      if (indexFileContent.trim().isEmpty()) {
+        return;
+      }
+      Set<String> autoIndexes = getIndexXmlStrings(indexFileContent);
       Set<String> missingIndexes = Sets.difference(autoIndexes, MANUAL_INDEXES);
       if (!missingIndexes.isEmpty()) {
         assert_().fail("Missing indexes:\n%s", Joiner.on('\n').join(missingIndexes));
       }
-    } catch (IOException e) {  // This is fine; no indexes were written.
+    } catch (IOException e) {
+      throw new RuntimeException(e);
     }
   }
 
@@ -352,12 +360,6 @@ public final class AppEngineRule extends ExternalResource {
       // To normalize the indexes, we are going to pass them through JSON and then rewrite the xml.
       JSONObject datastoreIndexes = new JSONObject();
       JSONObject indexFileObject = toJSONObject(indexFile);
-      if (!indexFileObject.has("datastore-indexes")) {
-        // Log for flaky appearance. We suspect that this is not a problem but need to inspect
-        // the content of this file to make sure.
-        // TODO(weiminyu): inspect file content and decide if this should be ignored.
-        logger.atWarning().log("Unexpected datastore-indexes-auto.xml:\n%s", indexFileObject);
-      }
       Object indexes = indexFileObject.get("datastore-indexes");
       if (indexes instanceof JSONObject) {
         datastoreIndexes = (JSONObject) indexes;
@@ -366,7 +368,8 @@ public final class AppEngineRule extends ExternalResource {
         builder.add(getIndexXmlString(index));
       }
     } catch (JSONException e) {
-      throw new RuntimeException(e);
+      throw new RuntimeException(
+          String.format("Error parsing datastore-indexes-auto.xml: [%s]", indexFile), e);
     }
     return builder.build();
   }

javatests/google/registry/testing/AppEngineRuleTest.java

@@ -0,0 +1,95 @@
+// Copyright 2019 The Nomulus Authors. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package google.registry.testing;
+
+import static google.registry.testing.JUnitBackports.assertThrows;
+import static java.nio.charset.StandardCharsets.UTF_8;
+
+import com.google.common.base.Joiner;
+import java.io.File;
+import java.io.IOException;
+import org.junit.Before;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.TemporaryFolder;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+/**
+ * Unit tests for {@link google.registry.testing.AppEngineRule}. Tests focus on Datastoe-related
+ * assertions made during teardown checks.
+ */
+@RunWith(JUnit4.class)
+public class AppEngineRuleTest {
+
+  // An arbitrary index in google/registry/env/common/default/WEB-INF/datastore-indexes.xml
+  private static final String DECLARED_INDEX =
+      Joiner.on('\n')
+          .join(
+              "<datastore-indexes autoGenerate=\"false\">",
+              "  <datastore-index kind=\"ContactResource\" ancestor=\"false\" source=\"manual\">",
+              "    <property name=\"currentSponsorClientId\" direction=\"asc\"/>",
+              "    <property name=\"deletionTime\" direction=\"asc\"/>",
+              "    <property name=\"searchName\" direction=\"asc\"/>",
+              "  </datastore-index>",
+              "</datastore-indexes>");
+  private static final String UNDECLARED_INDEX =
+      DECLARED_INDEX.replace("ContactResource", "NoSuchResource");
+
+  @Rule public TemporaryFolder temporaryFolder = new TemporaryFolder();
+
+  private final AppEngineRule appEngineRule = AppEngineRule.builder().withDatastore().build();
+
+  @Before
+  public void setupAppEngineRule() throws Exception {
+    appEngineRule.temporaryFolder = temporaryFolder;
+    appEngineRule.before();
+  }
+
+  @Test
+  public void testTeardown_successNoAutoIndexFile() {
+    appEngineRule.after();
+  }
+
+  @Test
+  public void testTeardown_successEmptyAutoIndexFile() throws Exception {
+    writeAutoIndexFile("");
+    appEngineRule.after();
+  }
+
+  @Test
+  public void testTeardown_successWhiteSpacesOnlyAutoIndexFile() throws Exception {
+    writeAutoIndexFile("  ");
+    appEngineRule.after();
+  }
+
+  @Test
+  public void testTeardown_successOnlyDeclaredIndexesUsed() throws Exception {
+    writeAutoIndexFile(DECLARED_INDEX);
+    appEngineRule.after();
+  }
+
+  @Test
+  public void testTeardown_failureUndeclaredIndexesUsed() throws Exception {
+    writeAutoIndexFile(UNDECLARED_INDEX);
+    assertThrows(AssertionError.class, () -> appEngineRule.after());
+  }
+
+  private void writeAutoIndexFile(String content) throws IOException {
+    com.google.common.io.Files.asCharSink(
+            new File(temporaryFolder.getRoot(), "datastore-indexes-auto.xml"), UTF_8)
+        .write(content);
+  }
+}

javatests/google/registry/testing/BUILD

@@ -5,10 +5,15 @@ package(
 
 licenses(["notice"])  # Apache 2.0
 
+load("//java/com/google/testing/builddefs:GenTestRules.bzl", "GenTestRules")
+
+TEST_CLASSES = ["AppEngineRuleTest.java"]
+
 java_library(
     name = "testing",
     srcs = glob(
         ["*.java"],
+        exclude = TEST_CLASSES,
     ),
     resources = [
         "logging.properties",
@@ -57,3 +62,22 @@ java_library(
         "@org_mockito_all",
     ],
 )
+
+java_library(
+    name = "tests",
+    srcs = TEST_CLASSES,
+    deps = [
+        ":testing",
+        "@com_google_guava",
+        "@junit",
+    ],
+)
+
+GenTestRules(
+    name = "GeneratedTestRules",
+    default_test_size = "small",
+    test_files = glob(["*Test.java"]),
+    deps = [
+        ":tests",
+    ],
+)