Make mvn verify work without install of spring-boot-dependencies

Previously, the custom layout sample could only be built successfully
if spring-boot-dependencies had be installed locally, making its
effective pom available in the local Maven cache.

This commit updates the sample's tests to look at its own pom to
determine the version of Spring Boot that should be used in the
Gradle tests.

Closes gh-8330

spring-boot-samples/spring-boot-sample-custom-layout/src/test/java/sample/layout/GradleIT.java

@@ -0,0 +1,90 @@
+/*
+ * Copyright 2012-2017 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
+ *
+ *      http://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 sample.layout;
+
+import java.io.File;
+import java.io.FileReader;
+
+import javax.xml.xpath.XPath;
+import javax.xml.xpath.XPathExpression;
+import javax.xml.xpath.XPathFactory;
+
+import org.gradle.tooling.GradleConnector;
+import org.gradle.tooling.ProjectConnection;
+import org.gradle.tooling.internal.consumer.DefaultGradleConnector;
+import org.junit.Test;
+import org.xml.sax.InputSource;
+
+import org.springframework.util.FileCopyUtils;
+
+public class GradleIT {
+
+	@Test
+	public void sampleDefault() throws Exception {
+		test("default", "sample");
+	}
+
+	@Test
+	public void sampleCustom() throws Exception {
+		test("custom", "custom");
+	}
+
+	private void test(String name, String expected) throws Exception {
+		File projectDirectory = new File("target/gradleit/" + name);
+		File javaDirectory = new File(
+				"target/gradleit/" + name + "/src/main/java/org/test/");
+		projectDirectory.mkdirs();
+		javaDirectory.mkdirs();
+		File script = new File(projectDirectory, "build.gradle");
+		FileCopyUtils.copy(new File("src/it/" + name + "/build.gradle"), script);
+		FileCopyUtils.copy(
+				new File("src/it/" + name
+						+ "/src/main/java/org/test/SampleApplication.java"),
+				new File(javaDirectory, "SampleApplication.java"));
+		GradleConnector gradleConnector = GradleConnector.newConnector();
+		gradleConnector.useGradleVersion("2.9");
+		((DefaultGradleConnector) gradleConnector).embedded(true);
+		ProjectConnection project = gradleConnector.forProjectDirectory(projectDirectory)
+				.connect();
+		project.newBuild().forTasks("clean", "build").setStandardOutput(System.out)
+				.setStandardError(System.err)
+				.withArguments("-PbootVersion=" + getBootVersion()).run();
+		Verify.verify(
+				new File("target/gradleit/" + name + "/build/libs/" + name + ".jar"),
+				expected);
+	}
+
+	public static String getBootVersion() {
+		return evaluateExpression(
+				"/*[local-name()='project']/*[local-name()='parent']/*[local-name()='version']"
+						+ "/text()");
+	}
+
+	private static String evaluateExpression(String expression) {
+		try {
+			XPathFactory xPathFactory = XPathFactory.newInstance();
+			XPath xpath = xPathFactory.newXPath();
+			XPathExpression expr = xpath.compile(expression);
+			String version = expr.evaluate(new InputSource(new FileReader("pom.xml")));
+			return version;
+		}
+		catch (Exception ex) {
+			throw new IllegalStateException("Failed to evaluate expression", ex);
+		}
+	}
+
+}