Polish "Test the Gradle plugin against Gradle 4.10.3 and 5.1.1"

Closes gh-15791

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/test/java/org/springframework/boot/gradle/junit/GradleCompatibilitySuite.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2018 the original author or authors.
+ * Copyright 2012-2019 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-tools/spring-boot-gradle-plugin/src/test/java/org/springframework/boot/gradle/plugin/KotlinPluginActionIntegrationTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2018 the original author or authors.
+ * Copyright 2012-2019 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.
@@ -43,12 +43,10 @@ public class KotlinPluginActionIntegrationTests {
 	}
 
 	@Test
-	public void kotlinVersionMatchesKotlinPluginVersion() {
+	public void kotlinVersionPropertyIsSet() {
 		String output = this.gradleBuild.build("kotlinVersion", "dependencies",
 				"--configuration", "compileClasspath").getOutput();
-		assertThat(output).contains("Kotlin version: 1.2.20");
-		assertThat(output)
-				.containsPattern("org.jetbrains.kotlin:kotlin-stdlib-jdk8:1.2.20");
+		assertThat(output).containsPattern("Kotlin version: [0-9]\\.[0-9]\\.[0-9]+");
 	}
 
 	@Test

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2018 the original author or authors.
+ * Copyright 2012-2019 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.