test: add it test for database default leader

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+/*
+* Copyright 2021 Google LLC
+*
+* 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 com.google.cloud.spanner.it;
+
+import static org.junit.Assert.assertEquals;
+
+import com.google.api.gax.paging.Page;
+import com.google.cloud.spanner.Database;
+import com.google.cloud.spanner.DatabaseAdminClient;
+import com.google.cloud.spanner.InstanceAdminClient;
+import com.google.cloud.spanner.InstanceConfig;
+import com.google.cloud.spanner.IntegrationTestEnv;
+import com.google.cloud.spanner.ParallelIntegrationTest;
+import java.time.Duration;
+import java.util.Collections;
+import java.util.List;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.TimeoutException;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+import java.util.stream.StreamSupport;
+import org.junit.After;
+import org.junit.Before;
+import org.junit.ClassRule;
+import org.junit.Test;
+import org.junit.experimental.categories.Category;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+@Category(ParallelIntegrationTest.class)
+@RunWith(JUnit4.class)
+public class ITDatabaseLeaderTest {
+
+public static final Duration WAIT_TIME = Duration.ofMinutes(5);
+@ClassRule public static IntegrationTestEnv env = new IntegrationTestEnv();
+
+private InstanceAdminClient instanceAdminClient;
+private DatabaseAdminClient databaseAdminClient;
+private String instanceId;
+private String databaseId;
+
+@Before
+public void setUp() {
+instanceId = env.getTestHelper().getInstanceId().getInstance();
+databaseId = env.getTestHelper().getUniqueDatabaseId();
+instanceAdminClient = env.getTestHelper().getClient().getInstanceAdminClient();
+databaseAdminClient = env.getTestHelper().getClient().getDatabaseAdminClient();
+}
+
+@After
+public void tearDown() {
+databaseAdminClient.dropDatabase(instanceId, databaseId);
+}
+
+@Test
+public void testCreateDatabaseWithDefaultLeader()
+throws InterruptedException, ExecutionException, TimeoutException {
+final Page<InstanceConfig> instanceConfigs = instanceAdminClient.listInstanceConfigs();
+final InstanceConfig instanceConfig = instanceConfigs.iterateAll().iterator().next();
+final List<String> leaderOptions = instanceConfig.getLeaderOptions();
+final String leader = leaderOptions.get(0);
+
+final Database createdDatabase =
+databaseAdminClient
+.createDatabase(
+instanceId,
+databaseId,
+Collections.singletonList(
+"ALTER DATABASE `"
++ databaseId
++ "` SET OPTIONS ( default_leader = '"
++ leader
++ "' )"))
+.get(WAIT_TIME.toMillis(), TimeUnit.MILLISECONDS);
+assertEquals(leader, createdDatabase.getDefaultLeader());
+
+final Database retrievedDatabase = databaseAdminClient.getDatabase(instanceId, databaseId);
+assertEquals(leader, retrievedDatabase.getDefaultLeader());
+
+final Database listedDatabase = listDatabasesWithId(databaseId).get(0);
+assertEquals(leader, listedDatabase.getDefaultLeader());
+}
+
+@Test
+public void testCreateDatabaseWithoutDefaultLeader()
+throws InterruptedException, ExecutionException, TimeoutException {
+final Database createdDatabase =
+databaseAdminClient
+.createDatabase(instanceId, databaseId, Collections.emptyList())
+.get(WAIT_TIME.toMillis(), TimeUnit.MILLISECONDS);
+assertEquals("", createdDatabase.getDefaultLeader());
+
+final Database retrievedDatabase = databaseAdminClient.getDatabase(instanceId, databaseId);
+assertEquals("", retrievedDatabase.getDefaultLeader());
+
+final Database listedDatabase = listDatabasesWithId(databaseId).get(0);
+assertEquals("", listedDatabase.getDefaultLeader());
+}
+
+private List<Database> listDatabasesWithId(String databaseId) {
+Page<Database> page = databaseAdminClient.listDatabases(instanceId);
+Stream<Database> stream = StreamSupport.stream(page.getValues().spliterator(), false);
+while (page.hasNextPage()) {
+page = page.getNextPage();
+stream = Stream.concat(stream, StreamSupport.stream(page.getValues().spliterator(), false));
+}
+
+return stream
+.filter(database -> database.getId().getDatabase().equals(databaseId))
+.collect(Collectors.toList());
+}
+}