Support parallel initialization of Testcontainers

Add support for a `spring.testcontainers.startup` property that can
be set to "sequential" or "parallel" to change how containers are
started.

Closes gh-37073

spring-boot-project/spring-boot-testcontainers/src/test/java/org/springframework/boot/testcontainers/lifecycle/TestcontainersLifecycleApplicationContextInitializerTests.java

@@ -16,13 +16,18 @@
 
 package org.springframework.boot.testcontainers.lifecycle;
 
+import java.util.Map;
+
 import org.junit.jupiter.api.Test;
 import org.testcontainers.containers.GenericContainer;
 import org.testcontainers.lifecycle.Startable;
 
+import org.springframework.beans.factory.config.BeanPostProcessor;
+import org.springframework.beans.factory.support.AbstractBeanFactory;
 import org.springframework.context.annotation.AnnotationConfigApplicationContext;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
+import org.springframework.core.env.MapPropertySource;
 
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.mockito.BDDMockito.given;
@@ -104,6 +109,22 @@ class TestcontainersLifecycleApplicationContextInitializerTests {
 		applicationContext.refresh();
 	}
 
+	@Test
+	void setupStartupBasedOnEnvironmentProperty() {
+		AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext();
+		applicationContext.getEnvironment()
+			.getPropertySources()
+			.addLast(new MapPropertySource("test", Map.of("spring.testcontainers.startup", "parallel")));
+		new TestcontainersLifecycleApplicationContextInitializer().initialize(applicationContext);
+		AbstractBeanFactory beanFactory = (AbstractBeanFactory) applicationContext.getBeanFactory();
+		BeanPostProcessor beanPostProcessor = beanFactory.getBeanPostProcessors()
+			.stream()
+			.filter(TestcontainersLifecycleBeanPostProcessor.class::isInstance)
+			.findFirst()
+			.get();
+		assertThat(beanPostProcessor).extracting("startup").isEqualTo(TestcontainersStartup.PARALLEL);
+	}
+
 	private AnnotationConfigApplicationContext createApplicationContext(Startable container) {
 		AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext();
 		new TestcontainersLifecycleApplicationContextInitializer().initialize(applicationContext);

spring-boot-project/spring-boot-testcontainers/src/test/java/org/springframework/boot/testcontainers/lifecycle/TestcontainersStartupTests.java

@@ -0,0 +1,122 @@
+/*
+ * Copyright 2012-2023 the original author or authors.
+ *
+ * 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
+ *
+ *      https://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 org.springframework.boot.testcontainers.lifecycle;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.concurrent.atomic.AtomicInteger;
+
+import org.junit.jupiter.api.Test;
+import org.testcontainers.lifecycle.Startable;
+
+import org.springframework.mock.env.MockEnvironment;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatIllegalArgumentException;
+
+/**
+ * Tests for {@link TestcontainersStartup}.
+ *
+ * @author Phillip Webb
+ */
+class TestcontainersStartupTests {
+
+	private static final String PROPERTY = TestcontainersStartup.PROPERTY;
+
+	private final AtomicInteger counter = new AtomicInteger();
+
+	@Test
+	void startWhenSquentialStartsSequentially() {
+		List<TestStartable> startables = createTestStartables(100);
+		TestcontainersStartup.SEQUENTIAL.start(startables);
+		for (int i = 0; i < startables.size(); i++) {
+			assertThat(startables.get(i).getIndex()).isEqualTo(i);
+			assertThat(startables.get(i).getThreadName()).isEqualTo(Thread.currentThread().getName());
+		}
+	}
+
+	@Test
+	void startWhenParallelStartsInParallel() {
+		List<TestStartable> startables = createTestStartables(100);
+		TestcontainersStartup.PARALLEL.start(startables);
+		assertThat(startables.stream().map(TestStartable::getThreadName)).hasSizeGreaterThan(1);
+	}
+
+	@Test
+	void getWhenNoPropertyReturnsDefault() {
+		MockEnvironment environment = new MockEnvironment();
+		assertThat(TestcontainersStartup.get(environment)).isEqualTo(TestcontainersStartup.SEQUENTIAL);
+	}
+
+	@Test
+	void getWhenPropertyReturnsBasedOnValue() {
+		MockEnvironment environment = new MockEnvironment();
+		assertThat(TestcontainersStartup.get(environment.withProperty(PROPERTY, "SEQUENTIAL")))
+			.isEqualTo(TestcontainersStartup.SEQUENTIAL);
+		assertThat(TestcontainersStartup.get(environment.withProperty(PROPERTY, "sequential")))
+			.isEqualTo(TestcontainersStartup.SEQUENTIAL);
+		assertThat(TestcontainersStartup.get(environment.withProperty(PROPERTY, "SEQuenTIaL")))
+			.isEqualTo(TestcontainersStartup.SEQUENTIAL);
+		assertThat(TestcontainersStartup.get(environment.withProperty(PROPERTY, "S-E-Q-U-E-N-T-I-A-L")))
+			.isEqualTo(TestcontainersStartup.SEQUENTIAL);
+		assertThat(TestcontainersStartup.get(environment.withProperty(PROPERTY, "parallel")))
+			.isEqualTo(TestcontainersStartup.PARALLEL);
+	}
+
+	@Test
+	void getWhenUnknownPropertyThrowsException() {
+		MockEnvironment environment = new MockEnvironment();
+		assertThatIllegalArgumentException()
+			.isThrownBy(() -> TestcontainersStartup.get(environment.withProperty(PROPERTY, "bad")))
+			.withMessage("Unknown 'spring.testcontainers.startup' property value 'bad'");
+	}
+
+	private List<TestStartable> createTestStartables(int size) {
+		List<TestStartable> testStartables = new ArrayList<>(size);
+		for (int i = 0; i < size; i++) {
+			testStartables.add(new TestStartable());
+		}
+		return testStartables;
+	}
+
+	private class TestStartable implements Startable {
+
+		private int index;
+
+		private String threadName;
+
+		@Override
+		public void start() {
+			this.index = TestcontainersStartupTests.this.counter.getAndIncrement();
+			this.threadName = Thread.currentThread().getName();
+		}
+
+		@Override
+		public void stop() {
+		}
+
+		int getIndex() {
+			return this.index;
+		}
+
+		String getThreadName() {
+			return this.threadName;
+		}
+
+	}
+
+}