Improve brave auto-configuration tests

See spring-projectsgh-30156

Author: mhalbritter

spring-boot-project/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/tracing/BraveAutoConfigurationTests.java

@@ -16,10 +16,12 @@
 
 package org.springframework.boot.actuate.autoconfigure.tracing;
 
+import brave.Tracing;
 import io.micrometer.tracing.brave.bridge.BraveTracer;
 import org.junit.jupiter.api.Test;
 
 import org.springframework.boot.autoconfigure.AutoConfigurations;
+import org.springframework.boot.test.context.FilteredClassLoader;
 import org.springframework.boot.test.context.runner.ApplicationContextRunner;
 
 import static org.assertj.core.api.Assertions.assertThat;
@@ -32,12 +34,23 @@
 class BraveAutoConfigurationTests {
 
 	private final ApplicationContextRunner contextRunner = new ApplicationContextRunner()
-			.withConfiguration(AutoConfigurations.of(MicrometerTracingAutoConfiguration.class,
-					ZipkinAutoConfiguration.class, BraveAutoConfiguration.class));
+			.withConfiguration(AutoConfigurations.of(BraveAutoConfiguration.class));
 
 	@Test
-	void hasBraveTracer() {
+	void shouldNotFailIfBraveIsMissing() {
+		this.contextRunner.withClassLoader(new FilteredClassLoader("brave"))
+				.run((context) -> assertThat(context).doesNotHaveBean(Tracing.class));
+	}
+
+	@Test
+	void shouldHaveBraveTracer() {
 		this.contextRunner.run((context) -> assertThat(context).hasSingleBean(BraveTracer.class));
 	}
 
+	@Test
+	void shouldNotFailIfMicrometerIsMissing() {
+		this.contextRunner.withClassLoader(new FilteredClassLoader("io.micrometer"))
+				.run((context) -> assertThat(context).doesNotHaveBean(BraveTracer.class));
+	}
+
 }