Remove default dependencies from test suite when folder does not exist

Resolves #40

Author: jjohannes

src/main/java/org/gradlex/javamodule/testing/JavaModuleTestingExtension.java

@@ -62,13 +62,20 @@ public JavaModuleTestingExtension(Project project) {
             if ("test".equals(jvmTestSuite.getName())) {
                 jvmTestSuite.useJUnitJupiter(); // override old Gradle convention to default to JUnit5 for all suites
             }
+
+            boolean testFolderExists = jvmTestSuite.getSources().getJava().getSrcDirs().stream().anyMatch(File::exists);
             if (isTestModule) {
                 blackbox(jvmTestSuite);
-            } else {
-                boolean testFolderExists = jvmTestSuite.getSources().getJava().getSrcDirs().stream().anyMatch(File::exists);
-                if (testFolderExists) {
-                    whitebox(jvmTestSuite, conf -> conf.getOpensTo().add("org.junit.platform.commons"));
-                }
+            } else if (testFolderExists) {
+                whitebox(jvmTestSuite, conf -> conf.getOpensTo().add("org.junit.platform.commons"));
+            }
+
+            // Remove the dependencies added by Gradle in case the test directory is missing. This allows the use of 'useJUnitJupiter("")' without hassle.
+            if (!testFolderExists) {
+                project.getConfigurations().getByName(jvmTestSuite.getSources().getImplementationConfigurationName(), implementation ->
+                        implementation.withDependencies(dependencySet -> dependencySet.removeIf(d -> "org.junit.jupiter".equals(d.getGroup()) && "junit-jupiter".equals(d.getName()))));
+                project.getConfigurations().getByName(jvmTestSuite.getSources().getRuntimeOnlyConfigurationName(), runtimeOnly ->
+                        runtimeOnly.withDependencies(dependencySet -> dependencySet.removeIf(d -> "org.junit.platform".equals(d.getGroup()) && "junit-platform-launcher".equals(d.getName()))));
             }
         });
     }

src/test/groovy/org/gradlex/javamodule/testing/test/CustomizationTest.groovy

@@ -101,4 +101,20 @@ class CustomizationTest extends Specification {
         then:
         result.task(":app:test").outcome == TaskOutcome.SUCCESS
     }
+
+    def "build does not fail when JUnit has no version and the test folder is empty"() {
+        given:
+        appTestModuleInfoFile.parentFile.deleteDir()
+        appBuildFile << '''
+            testing.suites.withType<JvmTestSuite>().all {
+                useJUnitJupiter("") // <- no version, we want to manage that ourselves
+            }
+        '''
+
+        when:
+        def result = runTests()
+
+        then:
+        result.task(":app:test").outcome == TaskOutcome.NO_SOURCE
+    }
 }