Verify that bootJar and bootWar handle duplicates gracefully

Closes gh-9573

spring-boot-tools/spring-boot-gradle-plugin/src/test/java/org/springframework/boot/gradle/tasks/bundling/AbstractBootArchiveIntegrationTests.java

@@ -115,4 +115,10 @@ public abstract class AbstractBootArchiveIntegrationTests {
 
 	}
 
+	@Test
+	public void duplicatesAreHandledGracefully() throws IOException {
+		assertThat(this.gradleBuild.build(this.taskName).task(":" + this.taskName)
+				.getOutcome()).isEqualTo(TaskOutcome.SUCCESS);
+	}
+
 }

spring-boot-tools/spring-boot-gradle-plugin/src/test/resources/org/springframework/boot/gradle/tasks/bundling/BootJarIntegrationTests-duplicatesAreHandledGracefully.gradle

@@ -0,0 +1,31 @@
+buildscript {
+	dependencies {
+		classpath files(pluginClasspath.split(','))
+	}
+}
+
+apply plugin: 'java'
+apply plugin: 'org.springframework.boot'
+
+bootJar {
+	mainClass = 'com.example.CustomMain'
+	duplicatesStrategy = "exclude"
+}
+
+configurations {
+	provided
+}
+
+sourceSets.all {
+	compileClasspath += configurations.provided
+	runtimeClasspath += configurations.provided
+}
+
+repositories {
+	maven { url "https://repo.spring.io/libs-snapshot" }
+}
+
+dependencies {
+	compile "org.apache.commons:commons-lang3:3.6"
+	provided "org.apache.commons:commons-lang3:3.6"
+}