Add cross-version testing

Author: jjohannes

build.gradle.kts

@@ -6,7 +6,7 @@ group = "org.gradlex"
 version = "1.0.1"
 
 java {
-    toolchain.languageVersion = JavaLanguageVersion.of(21)
+    toolchain.languageVersion = JavaLanguageVersion.of(17)
 }
 
 tasks.compileJava {
@@ -29,6 +29,15 @@ pluginPublishConventions {
 
 testing.suites.named<JvmTestSuite>("test") {
     useJUnitJupiter()
+    listOf("7.4", "7.6.5", "8.0.2", "8.14.2").forEach { gradleVersionUnderTest ->
+        targets.register("test${gradleVersionUnderTest}") {
+            testTask {
+                group = LifecycleBasePlugin.VERIFICATION_GROUP
+                description = "Runs tests against Gradle $gradleVersionUnderTest"
+                systemProperty("gradleVersionUnderTest", gradleVersionUnderTest)
+            }
+        }
+    }
     dependencies {
         implementation("org.assertj:assertj-core:3.27.3")
     }

src/test/java/org/gradlex/javamodule/packaging/test/JavaModulePackagingTest.java

@@ -53,16 +53,16 @@ void can_use_plugin(String label, String os, boolean success) {
                     version = "1.0"
                     javaModulePackaging {
                         target("macos") {
-                            operatingSystem = "macos"
-                            architecture = "%s"
+                            operatingSystem.set("macos")
+                            architecture.set("%s")
                         }
                         target("ubuntu") {
-                            operatingSystem = "linux"
-                            architecture = "x86-64"
+                            operatingSystem.set("linux")
+                            architecture.set("x86-64")
                         }
                         target("windows") {
-                            operatingSystem = "windows"
-                            architecture = "x86-64"
+                            operatingSystem.set("windows")
+                            architecture.set("x86-64")
                         }
                     }
                 """.formatted(macosArch));

src/test/java/org/gradlex/javamodule/packaging/test/fixture/GradleBuild.java

@@ -42,14 +42,10 @@ public class GradleBuild {
     public static final String GRADLE_VERSION_UNDER_TEST = System.getProperty("gradleVersionUnderTest");
 
     public GradleBuild() {
-        this(false, createBuildTmpDir());
+        this(createBuildTmpDir());
     }
 
-    public GradleBuild(boolean withHelpTasks) {
-        this(withHelpTasks, createBuildTmpDir());
-    }
-
-    public GradleBuild(boolean withHelpTasks, Path dir) {
+    public GradleBuild(Path dir) {
         this.projectDir = new Directory(dir);
         this.settingsFile = file("settings.gradle.kts");
         this.appBuildFile = file("app/build.gradle.kts");
@@ -74,6 +70,9 @@ public GradleBuild(boolean withHelpTasks, Path dir) {
                 id("application")
             }
             group = "org.example"
+            java {
+                toolchain.languageVersion.set(JavaLanguageVersion.of(17))
+            }
             application {
                 mainModule.set("org.example.app")
                 mainClass.set("org.example.app.Main")