Assert a JSR validator is created if a Spring validator is defined

This commit restores and adds tests that validates
`ValidationAutoConfiguration` will configure a JSR validator even if a
Spring Validator is present.

Closes spring-projectsgh-8976

Author: snicoll

spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/validation/ValidationAutoConfigurationTests.java

@@ -32,14 +32,18 @@
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.validation.annotation.Validated;
+import org.springframework.validation.beanvalidation.LocalValidatorFactoryBean;
 import org.springframework.validation.beanvalidation.MethodValidationPostProcessor;
+import org.springframework.validation.beanvalidation.OptionalValidatorFactoryBean;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.Mockito.mock;
 
 /**
  * Tests for {@link ValidationAutoConfiguration}.
  *
  * @author Stephane Nicoll
+ * @author Phillip Webb
  */
 public class ValidationAutoConfigurationTests {
 
@@ -55,6 +59,62 @@ public void close() {
 		}
 	}
 
+	@Test
+	public void validationAutoConfigurationShouldConfigureDefaultValidator() {
+		load(Config.class);
+		String[] jsrValidatorNames = this.context.getBeanNamesForType(Validator.class);
+		String[] springValidatorNames = this.context
+				.getBeanNamesForType(org.springframework.validation.Validator.class);
+		assertThat(jsrValidatorNames).containsExactly("defaultValidator");
+		assertThat(springValidatorNames).containsExactly("defaultValidator");
+		Validator jsrValidator = this.context.getBean(Validator.class);
+		org.springframework.validation.Validator springValidator = this.context
+				.getBean(org.springframework.validation.Validator.class);
+		assertThat(jsrValidator).isInstanceOf(LocalValidatorFactoryBean.class);
+		assertThat(jsrValidator).isEqualTo(springValidator);
+	}
+
+	@Test
+	public void validationAutoConfigurationWhenUserProvidesValidatorShouldBackOff() {
+		load(UserDefinedValidatorConfig.class);
+		String[] jsrValidatorNames = this.context.getBeanNamesForType(Validator.class);
+		String[] springValidatorNames = this.context
+				.getBeanNamesForType(org.springframework.validation.Validator.class);
+		assertThat(jsrValidatorNames).containsExactly("customValidator");
+		assertThat(springValidatorNames).containsExactly("customValidator");
+		org.springframework.validation.Validator springValidator = this.context
+				.getBean(org.springframework.validation.Validator.class);
+		Validator jsrValidator = this.context.getBean(Validator.class);
+		assertThat(jsrValidator).isInstanceOf(OptionalValidatorFactoryBean.class);
+		assertThat(jsrValidator).isEqualTo(springValidator);
+	}
+
+	@Test
+	public void validationAutoConfigurationWhenUserProvidesJsrValidatorShouldBackOff() {
+		load(UserDefinedJsrValidatorConfig.class);
+		String[] jsrValidatorNames = this.context.getBeanNamesForType(Validator.class);
+		String[] springValidatorNames = this.context
+				.getBeanNamesForType(org.springframework.validation.Validator.class);
+		assertThat(jsrValidatorNames).containsExactly("customValidator");
+		assertThat(springValidatorNames).isEmpty();
+	}
+
+	@Test
+	public void validationAutoConfigurationWhenUserProvidesSpringValidatorShouldCreateJsrValidator() {
+		load(UserDefinedSpringValidatorConfig.class);
+		String[] jsrValidatorNames = this.context.getBeanNamesForType(Validator.class);
+		String[] springValidatorNames = this.context
+				.getBeanNamesForType(org.springframework.validation.Validator.class);
+		assertThat(jsrValidatorNames).containsExactly("defaultValidator");
+		assertThat(springValidatorNames)
+				.containsExactly("customValidator", "defaultValidator");
+		Validator jsrValidator = this.context.getBean(Validator.class);
+		org.springframework.validation.Validator springValidator = this.context
+				.getBean(org.springframework.validation.Validator.class);
+		assertThat(jsrValidator).isInstanceOf(LocalValidatorFactoryBean.class);
+		assertThat(jsrValidator).isEqualTo(springValidator);
+	}
+
 	@Test
 	public void validationIsEnabled() {
 		load(SampleService.class);
@@ -115,6 +175,41 @@ public void load(Class<?> config, String... environment) {
 		this.context = ctx;
 	}
 
+	@Configuration
+	static class Config {
+
+	}
+
+	@Configuration
+	static class UserDefinedValidatorConfig {
+
+		@Bean
+		public OptionalValidatorFactoryBean customValidator() {
+			return new OptionalValidatorFactoryBean();
+		}
+
+	}
+
+	@Configuration
+	static class UserDefinedJsrValidatorConfig {
+
+		@Bean
+		public Validator customValidator() {
+			return mock(Validator.class);
+		}
+
+	}
+
+	@Configuration
+	static class UserDefinedSpringValidatorConfig {
+
+		@Bean
+		public org.springframework.validation.Validator customValidator() {
+			return mock(org.springframework.validation.Validator.class);
+		}
+
+	}
+
 	@Validated
 	static class SampleService {