Fail fast when plugin is used with an unsupported version of Gradle

Closes gh-8820

spring-boot-tools/spring-boot-gradle-plugin/src/test/java/org/springframework/boot/gradle/plugin/SpringBootPluginIntegrationTests.java

@@ -0,0 +1,54 @@
+/*
+ * 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 org.springframework.boot.gradle.plugin;
+
+import org.gradle.testkit.runner.BuildResult;
+import org.junit.Rule;
+import org.junit.Test;
+
+import org.springframework.boot.gradle.testkit.GradleBuild;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Integration tests for {@link SpringBootPlugin}.
+ *
+ * @author Andy Wilkinson
+ */
+public class SpringBootPluginIntegrationTests {
+
+	@Rule
+	public final GradleBuild gradleBuild = new GradleBuild();
+
+	@Test
+	public void failFastWithVersionOfGradleLowerThanRequired() {
+		BuildResult result = this.gradleBuild.gradleVersion("3.3").buildAndFail();
+		assertThat(result.getOutput()).contains("Spring Boot plugin requires Gradle 3.4"
+				+ " or later. The current version is Gradle 3.3");
+	}
+
+	@Test
+	public void succeedWithVersionOfGradleHigherThanRequired() {
+		this.gradleBuild.gradleVersion("3.5-rc-3").build();
+	}
+
+	@Test
+	public void succeedWithVersionOfGradleMatchingWhatIsRequired() {
+		this.gradleBuild.gradleVersion("3.4").build();
+	}
+
+}

spring-boot-tools/spring-boot-gradle-plugin/src/test/java/org/springframework/boot/gradle/testkit/GradleBuild.java

@@ -55,6 +55,8 @@ public class GradleBuild implements TestRule {
 
 	private String script;
 
+	private String gradleVersion;
+
 	@Override
 	public Statement apply(Statement base, Description description) {
 		URL scriptUrl = findDefaultScript(description);
@@ -149,6 +151,9 @@ public class GradleBuild implements TestRule {
 				new FileWriter(new File(this.projectDir, "build.gradle")));
 		GradleRunner gradleRunner = GradleRunner.create().withProjectDir(this.projectDir)
 				.forwardOutput();
+		if (this.gradleVersion != null) {
+			gradleRunner.withGradleVersion(this.gradleVersion);
+		}
 		List<String> allArguments = new ArrayList<String>();
 		allArguments.add("-PpluginClasspath=" + pluginClasspath());
 		allArguments.add("-PbootVersion=" + getBootVersion());
@@ -164,6 +169,11 @@ public class GradleBuild implements TestRule {
 		this.projectDir = projectDir;
 	}
 
+	public GradleBuild gradleVersion(String version) {
+		this.gradleVersion = version;
+		return this;
+	}
+
 	private static String getBootVersion() {
 		return evaluateExpression(
 				"/*[local-name()='project']/*[local-name()='parent']/*[local-name()='version']"