Treat ALL-DEFAULT runtime modules as root modules.

JUnit Jupiter Engine now "requires java.scripting" which is not resolved
by default -- at least on OpenJDK 10.

Details at http://mail.openjdk.java.net/pipermail/jigsaw-dev/2018-February/thread.html#13574
Related issue #1282

Author: sormuras

junit-platform-commons-java-9/junit-platform-commons-java-9.gradle

@@ -54,7 +54,7 @@ task execScanModulepath(type: Exec, dependsOn: [generateDependenciesDirectory, g
 					generateDependenciesDirectory.destinationDir,
 					generateIntegrationTestsJar.archivePath
 				).asPath,
-			'--add-modules', 'ALL-MODULE-PATH',
+			'--add-modules', 'ALL-MODULE-PATH,ALL-DEFAULT',
 			'--module', 'org.junit.platform.console',
 			'--scan-modules'
 	]

junit-platform-gradle-plugin/src/main/groovy/org/junit/platform/gradle/plugin/JUnitPlatformPlugin.groovy

@@ -134,8 +134,10 @@ class JUnitPlatformPlugin implements Plugin<Project> {
 					jvmArgs += ['--module-path', junitExtension.modulepath.asPath]
 				}
 				// Treat all modules on the path as root modules.
+				// Also add all default modules, needed on OpenJDK to resolve "java.scripting".
+				// See http://mail.openjdk.java.net/pipermail/jigsaw-dev/2018-February/thread.html#13574
 				if (!jvmArgs.contains('--add-modules')) {
-					jvmArgs += ['--add-modules', 'ALL-MODULE-PATH']
+					jvmArgs += ['--add-modules', 'ALL-MODULE-PATH,ALL-DEFAULT']
 				}
 				// Set main class name to '--module' (https://github.com/junit-team/junit5/issues/1234)
 				// The first argument will be 'org.junit.platform.console'

junit-platform-gradle-plugin/src/test/groovy/org/junit/platform/gradle/plugin/JUnitPlatformPluginSpec.groovy

@@ -224,7 +224,7 @@ class JUnitPlatformPluginSpec extends Specification {
 		junitTask instanceof JavaExec
 
 		junitTask.jvmArgs.containsAll('--module-path', project.files("abc.jar").asPath)
-		junitTask.jvmArgs.containsAll('--add-modules', 'ALL-MODULE-PATH')
+		junitTask.jvmArgs.containsAll('--add-modules', 'ALL-MODULE-PATH,ALL-DEFAULT')
 		junitTask.main == '--module'
 		junitTask.args[0] == 'org.junit.platform.console'
 		junitTask.args.contains('--scan-modules')