Polish "Add auto-configuration for DiskSpaceMetrics"

See gh-26001

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/metrics/JvmMetricsAutoConfiguration.java

 /*
- * Copyright 2012-2020 the original author or authors.
+ * Copyright 2012-2021 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.

spring-boot-project/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/metrics/JvmMetricsAutoConfigurationTests.java

 /*
- * Copyright 2012-2019 the original author or authors.
+ * Copyright 2012-2021 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.
@@ -27,7 +27,9 @@ import org.junit.jupiter.api.Test;
 
 import org.springframework.boot.actuate.autoconfigure.metrics.test.MetricsRun;
 import org.springframework.boot.autoconfigure.AutoConfigurations;
+import org.springframework.boot.test.context.assertj.AssertableApplicationContext;
 import org.springframework.boot.test.context.runner.ApplicationContextRunner;
+import org.springframework.boot.test.context.runner.ContextConsumer;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 
@@ -47,53 +49,43 @@ class JvmMetricsAutoConfigurationTests {
 
 	@Test
 	void autoConfiguresJvmMetrics() {
-		this.contextRunner.run((context) -> assertThat(context).hasSingleBean(JvmGcMetrics.class)
-				.hasSingleBean(JvmMemoryMetrics.class).hasSingleBean(JvmThreadMetrics.class)
-				.hasSingleBean(ClassLoaderMetrics.class).hasSingleBean(DiskSpaceMetrics.class));
+		this.contextRunner.run(assertMetricsBeans());
 	}
 
 	@Test
 	void allowsCustomJvmGcMetricsToBeUsed() {
 		this.contextRunner.withUserConfiguration(CustomJvmGcMetricsConfiguration.class)
-				.run((context) -> assertThat(context).hasSingleBean(JvmGcMetrics.class).hasBean("customJvmGcMetrics")
-						.hasSingleBean(JvmMemoryMetrics.class).hasSingleBean(JvmThreadMetrics.class)
-						.hasSingleBean(ClassLoaderMetrics.class).hasSingleBean(DiskSpaceMetrics.class));
+				.run(assertMetricsBeans().andThen((context) -> assertThat(context).hasBean("customJvmGcMetrics")));
 	}
 
 	@Test
 	void allowsCustomJvmMemoryMetricsToBeUsed() {
 		this.contextRunner.withUserConfiguration(CustomJvmMemoryMetricsConfiguration.class)
-				.run((context) -> assertThat(context).hasSingleBean(JvmGcMetrics.class)
-						.hasSingleBean(JvmMemoryMetrics.class).hasBean("customJvmMemoryMetrics")
-						.hasSingleBean(JvmThreadMetrics.class).hasSingleBean(ClassLoaderMetrics.class)
-						.hasSingleBean(DiskSpaceMetrics.class));
+				.run(assertMetricsBeans().andThen((context) -> assertThat(context).hasBean("customJvmMemoryMetrics")));
 	}
 
 	@Test
 	void allowsCustomJvmThreadMetricsToBeUsed() {
 		this.contextRunner.withUserConfiguration(CustomJvmThreadMetricsConfiguration.class)
-				.run((context) -> assertThat(context).hasSingleBean(JvmGcMetrics.class)
-						.hasSingleBean(JvmMemoryMetrics.class).hasSingleBean(JvmThreadMetrics.class)
-						.hasBean("customJvmThreadMetrics").hasSingleBean(ClassLoaderMetrics.class)
-						.hasSingleBean(DiskSpaceMetrics.class));
+				.run(assertMetricsBeans().andThen((context) -> assertThat(context).hasBean("customJvmThreadMetrics")));
 	}
 
 	@Test
 	void allowsCustomClassLoaderMetricsToBeUsed() {
-		this.contextRunner.withUserConfiguration(CustomClassLoaderMetricsConfiguration.class)
-				.run((context) -> assertThat(context).hasSingleBean(JvmGcMetrics.class)
-						.hasSingleBean(JvmMemoryMetrics.class).hasSingleBean(JvmThreadMetrics.class)
-						.hasSingleBean(ClassLoaderMetrics.class).hasBean("customClassLoaderMetrics")
-						.hasSingleBean(DiskSpaceMetrics.class));
+		this.contextRunner.withUserConfiguration(CustomClassLoaderMetricsConfiguration.class).run(
+				assertMetricsBeans().andThen((context) -> assertThat(context).hasBean("customClassLoaderMetrics")));
 	}
 
 	@Test
 	void allowsCustomDiskSpaceMetricsToBeUsed() {
 		this.contextRunner.withUserConfiguration(CustomDiskSpaceMetricsConfiguration.class)
-				.run((context) -> assertThat(context).hasSingleBean(JvmGcMetrics.class)
-						.hasSingleBean(JvmMemoryMetrics.class).hasSingleBean(JvmThreadMetrics.class)
-						.hasSingleBean(ClassLoaderMetrics.class).hasSingleBean(DiskSpaceMetrics.class)
-						.hasBean("customDiskSpaceMetrics"));
+				.run(assertMetricsBeans().andThen((context) -> assertThat(context).hasBean("customDiskSpaceMetrics")));
+	}
+
+	private ContextConsumer<AssertableApplicationContext> assertMetricsBeans() {
+		return (context) -> assertThat(context).hasSingleBean(JvmGcMetrics.class).hasSingleBean(JvmMemoryMetrics.class)
+				.hasSingleBean(JvmThreadMetrics.class).hasSingleBean(ClassLoaderMetrics.class)
+				.hasSingleBean(DiskSpaceMetrics.class);
 	}
 
 	@Configuration(proxyBeanMethods = false)