Improve error information in coverage test. (#537)

* Improve error information in coverage test.

If the golden schema isn't up-to-date with the persistence model, the coverage
tests fail with an exception chain that ends in a PSQLException 'relation
"TableName" does not exist' which is kind of misleading when the problem is
that your golden schema isn't up-to-date.

Check for this error in the coverage tests and generate a more informative
error message indicating a likely root cause.

core/src/test/java/google/registry/persistence/transaction/JpaEntityCoverage.java

@@ -23,6 +23,7 @@ import com.google.common.collect.ImmutableSet;
 import com.google.common.collect.Maps;
 import com.google.common.collect.Sets;
 import google.registry.persistence.PersistenceXmlUtility;
+import java.sql.SQLException;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
@@ -96,6 +97,7 @@ public class JpaEntityCoverage extends ExternalResource {
    * @return true if an instance of {@code entityType} is found in the database and can be read
    */
   private static boolean isPersisted(Class entityType) {
+    try {
       List result =
           jpaTm()
               .transact(
@@ -108,6 +110,21 @@ public class JpaEntityCoverage extends ExternalResource {
                           .setMaxResults(1)
                           .getResultList());
       return !result.isEmpty() && entityType.isInstance(result.get(0));
+    } catch (RuntimeException e) {
+      // See if this was caused by a "relation does not exist" error.
+      Throwable cause = e;
+      while ((cause = cause.getCause()) != null) {
+        if (cause instanceof SQLException
+            && cause.getMessage().matches("(?s).*relation .* does not exist.*")) {
+          throw new RuntimeException(
+              "SQLException occurred.  If you've updated the set of entities, make sure you've "
+                  + "also updated the golden schema.  See db/README.md for details.",
+              e);
+        }
+      }
+
+      throw e;
+    }
   }
 
   private static String getJpaEntityName(Class entityType) {