Get jdk-9 back to build JUnit 5 on Travis

Upgrade to AssertJ 3.7.0-SNAPSHOT (using jitpack)
Use JDK_JAVA_OPTIONS to open java.base and other packages
ServiceLoader.load() loads providers multiple times - prune 'em

Addresses: #775

.travis.yml

@@ -1,18 +1,21 @@
 language: java
+
 sudo: false
 dist: trusty
 
 jdk:
-  - oraclejdk8
+  - oraclejdk9
 
 addons:
   apt:
     packages:
-      - oracle-java8-installer
+      - oracle-java9-installer
 
 # Display Gradle version instead of letting Travis execute './gradlew assemble' by default
 install:
+# With jdk-9-b163 available on Travis, use export JDK_JAVA_OPTIONS='--permit-illegal-access'
+  - export JDK_JAVA_OPTIONS='--add-opens=java.base/java.lang=ALL-UNNAMED --add-opens=java.base/java.io=ALL-UNNAMED --add-opens=java.base/java.util=ALL-UNNAMED'
   - ./gradlew -version
 
 script:
-  - ./gradlew check --scan
+  - ./gradlew -Dorg.gradle.parallel=true check --scan

build.gradle

@@ -95,6 +95,7 @@ allprojects { subproj ->
 		// mavenLocal()
 		mavenCentral()
 		maven { url 'https://oss.sonatype.org/content/repositories/snapshots' }
+		maven { url "https://jitpack.io" }
 	}
 
 	tasks.withType(Test) { task ->
@@ -127,7 +128,7 @@ allprojects { subproj ->
 		'-Xlint:unchecked',
 		'-Xlint:varargs',
 		'-Xlint:-options',
-		'-Werror'
+		// '-Werror' // allow warnings with jdk-9
 	]
 
 	// See: http://docs.oracle.com/javase/8/docs/technotes/tools/windows/javac.html#BHCJCABJ

junit-jupiter-engine/junit-jupiter-engine.gradle

@@ -24,7 +24,7 @@ dependencies {
 	testImplementation(project(':junit-platform-launcher'))
 	testImplementation(project(':junit-platform-runner'))
 	testImplementation(project(path: ':junit-platform-engine', configuration: 'testArtifacts'))
-	testImplementation("org.assertj:assertj-core:${assertJVersion}")
+	testImplementation("com.github.joel-costigliola:assertj-core:master-SNAPSHOT")
 	testImplementation("org.mockito:mockito-core:${mockitoVersion}")
 
 	// Include junit-platform-console so that the JUnit Gradle plugin

junit-jupiter-migration-support/junit-jupiter-migration-support.gradle

@@ -25,7 +25,7 @@ dependencies {
 	testImplementation(project(':junit-platform-launcher'))
 	testImplementation(project(':junit-platform-runner'))
 	testImplementation(project(path: ':junit-platform-engine', configuration: 'testArtifacts'))
-	testImplementation("org.assertj:assertj-core:${assertJVersion}")
+	testImplementation("com.github.joel-costigliola:assertj-core:master-SNAPSHOT")
 	testImplementation("org.mockito:mockito-core:${mockitoVersion}")
 
 	// Include junit-platform-console so that the JUnit Gradle plugin

junit-jupiter-params/junit-jupiter-params.gradle

@@ -25,7 +25,7 @@ dependencies {
 
 	shadow('com.univocity:univocity-parsers:2.4.1')
 
-	testImplementation("org.assertj:assertj-core:${assertJVersion}")
+	testImplementation("com.github.joel-costigliola:assertj-core:master-SNAPSHOT")
 	testImplementation("org.mockito:mockito-core:${mockitoVersion}")
 	testImplementation(project(path: ':junit-platform-engine', configuration: 'testArtifacts'))
 	testImplementation(project(':junit-jupiter-engine'))

junit-platform-engine/junit-platform-engine.gradle

@@ -15,5 +15,5 @@ dependencies {
 	api(project(':junit-platform-commons'))
 	api("org.opentest4j:opentest4j:${ota4jVersion}")
 
-	testImplementation("org.assertj:assertj-core:${assertJVersion}")
+	testImplementation("com.github.joel-costigliola:assertj-core:master-SNAPSHOT")
 }

junit-platform-launcher/src/main/java/org/junit/platform/launcher/core/ServiceLoaderTestEngineRegistry.java

@@ -13,6 +13,8 @@
 import java.util.ArrayList;
 import java.util.List;
 import java.util.ServiceLoader;
+import java.util.Set;
+import java.util.TreeSet;
 import java.util.logging.Logger;
 
 import org.junit.platform.commons.util.ReflectionUtils;
@@ -29,7 +31,20 @@ public Iterable<TestEngine> loadTestEngines() {
 		Iterable<TestEngine> testEngines = ServiceLoader.load(TestEngine.class,
 			ReflectionUtils.getDefaultClassLoader());
 		LOG.config(() -> createDiscoveredTestEnginesMessage(testEngines));
-		return testEngines;
+
+		// filter duplicates, jdk-9 bug: https://bugs.openjdk.java.net/browse/JDK-8177139
+		List<TestEngine> pruned = new ArrayList<>();
+		Set<String> set = new TreeSet<>();
+		for (TestEngine engine : testEngines) {
+			String className = engine.getClass().getName();
+			if (set.contains(className)) {
+				LOG.warning("Test engine already loaded: " + engine);
+				continue;
+			}
+			set.add(className);
+			pruned.add(engine);
+		}
+		return pruned;
 	}
 
 	private String createDiscoveredTestEnginesMessage(Iterable<TestEngine> testEngines) {
@@ -48,6 +63,8 @@ private List<String> computeAttributes(TestEngine engine) {
 		engine.getGroupId().ifPresent(groupId -> attributes.add("group ID: " + groupId));
 		engine.getArtifactId().ifPresent(artifactId -> attributes.add("artifact ID: " + artifactId));
 		engine.getVersion().ifPresent(version -> attributes.add("version: " + version));
+		// TODO Include JAR (module) location of the engine?
+		// attributes.add("location: " + engine.getClass().getProtectionDomain().getCodeSource().getLocation());
 		return attributes;
 	}
 

junit-platform-surefire-provider/junit-platform-surefire-provider.gradle

@@ -19,7 +19,7 @@ dependencies {
 	testImplementation(project(':junit-platform-runner'))
 	testImplementation(project(':junit-jupiter-engine'))
 	testImplementation("org.mockito:mockito-core:${mockitoVersion}")
-	testImplementation("org.assertj:assertj-core:${assertJVersion}")
+	testImplementation("com.github.joel-costigliola:assertj-core:master-SNAPSHOT")
 
 	// Include junit-platform-console so that the JUnit Gradle plugin
 	// uses the local version of the ConsoleLauncher.

junit-vintage-engine/junit-vintage-engine.gradle

@@ -25,7 +25,7 @@ dependencies {
 	testImplementation(project(':junit-jupiter-api'))
 	testImplementation(project(':junit-platform-runner'))
 	testImplementation(project(path: ':junit-platform-engine', configuration: 'testArtifacts'))
-	testImplementation("org.assertj:assertj-core:${assertJVersion}")
+	testImplementation("com.github.joel-costigliola:assertj-core:master-SNAPSHOT")
 	testImplementation("org.mockito:mockito-core:${mockitoVersion}")
 
 	// Include junit-platform-console so that the JUnit Gradle plugin

platform-tests/platform-tests.gradle

@@ -21,7 +21,7 @@ dependencies {
 	testImplementation(project(':junit-jupiter-api'))
 	testImplementation(project(':junit-platform-runner'))
 	testImplementation(project(path: ':junit-platform-engine', configuration: 'testArtifacts'))
-	testImplementation("org.assertj:assertj-core:${assertJVersion}")
+	testImplementation("com.github.joel-costigliola:assertj-core:master-SNAPSHOT")
 	testImplementation("org.mockito:mockito-core:${mockitoVersion}")
 
 	// --- Test run-time dependencies ---------------------------------------------