Add a test to verify persistence.xml (#482)

core/src/test/java/google/registry/persistence/PersistenceXmlTest.java

@@ -0,0 +1,67 @@
+// Copyright 2020 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.persistence;
+
+import static com.google.common.collect.ImmutableList.toImmutableList;
+import static com.google.common.collect.ImmutableSet.toImmutableSet;
+
+import com.google.common.collect.ImmutableList;
+import com.google.common.collect.ImmutableSet;
+import com.google.common.truth.Expect;
+import java.util.Collections;
+import javax.persistence.AttributeConverter;
+import javax.persistence.Entity;
+import org.junit.ClassRule;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+/** Unit tests to verify persistence.xml is valid. */
+@RunWith(JUnit4.class)
+public class PersistenceXmlTest {
+
+  @ClassRule public static final Expect expect = Expect.create();
+
+  @Test
+  public void verifyClassTags_containOnlyRequiredClasses() {
+    ImmutableList<Class> managedClassed = PersistenceXmlUtility.getManagedClasses();
+
+    ImmutableList<Class> unnecessaryClasses =
+        managedClassed.stream()
+            .filter(
+                clazz ->
+                    !clazz.isAnnotationPresent(Entity.class)
+                        && !AttributeConverter.class.isAssignableFrom(clazz))
+            .collect(toImmutableList());
+
+    ImmutableSet<Class> duplicateClasses =
+        managedClassed.stream()
+            .filter(clazz -> Collections.frequency(managedClassed, clazz) > 1)
+            .collect(toImmutableSet());
+
+    expect
+        .withMessage("Found duplicate <class> tags defined in persistence.xml.")
+        .that(duplicateClasses)
+        .isEmpty();
+
+    expect
+        .withMessage(
+            "Found unnecessary <class> tags defined in persistence.xml. Only entity class and"
+                + " implementation of AttributeConverter are required to be added in"
+                + " persistence.xml.")
+        .that(unnecessaryClasses)
+        .isEmpty();
+  }
+}