diff --git a/com.avaloq.tools.ddk.check.core.test/META-INF/MANIFEST.MF b/com.avaloq.tools.ddk.check.core.test/META-INF/MANIFEST.MF
index 3c5df2d214..cb6fc23968 100644
--- a/com.avaloq.tools.ddk.check.core.test/META-INF/MANIFEST.MF
+++ b/com.avaloq.tools.ddk.check.core.test/META-INF/MANIFEST.MF
@@ -20,7 +20,6 @@ Require-Bundle: com.avaloq.tools.ddk.check.core,
  org.eclipse.xtend.lib,
  org.eclipse.xtext.ui.testing,
  org.eclipse.xtext.testing,
- org.junit,
  org.mockito.mockito-core,
  com.avaloq.tools.ddk.check.runtime.core,
  org.eclipse.ui.workbench;resolution:=optional,
@@ -31,15 +30,11 @@ Require-Bundle: com.avaloq.tools.ddk.check.core,
  org.eclipse.xtext.xbase.testing,
  junit-jupiter-api,
  junit-jupiter-engine,
- junit-vintage-engine
+ junit-vintage-engine,
+ junit-platform-suite-api
 Export-Package: com.avaloq.tools.ddk.check.core.test,
  com.avaloq.tools.ddk.check.core.test.util,
  com.avaloq.tools.ddk.check.test.core,
  com.avaloq.tools.ddk.check
-Import-Package: org.junit.runner;version="4.5.0",
- org.junit.runner.manipulation;version="4.5.0",
- org.junit.runner.notification;version="4.5.0",
- org.junit.runners;version="4.5.0",
- org.junit.runners.model;version="4.5.0",
- org.hamcrest.core
+Import-Package: org.hamcrest.core
 Automatic-Module-Name: com.avaloq.tools.ddk.check.core.test
diff --git a/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/core/generator/IssueCodeValueTest.xtend b/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/core/generator/IssueCodeValueTest.xtend
index 26ad426597..7a53cffd08 100644
--- a/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/core/generator/IssueCodeValueTest.xtend
+++ b/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/core/generator/IssueCodeValueTest.xtend
@@ -12,17 +12,18 @@
 package com.avaloq.tools.ddk.check.core.generator
 
 import org.eclipse.xtext.testing.InjectWith
-import org.junit.runner.RunWith
 import com.avaloq.tools.ddk.check.CheckInjectorProvider
-import org.eclipse.xtext.testing.XtextRunner
 import com.avaloq.tools.ddk.check.core.test.AbstractCheckGenerationTestCase
-import org.junit.Test
 import java.util.List
 import org.eclipse.xtext.xbase.testing.JavaSource
 import java.io.ByteArrayInputStream
+import org.junit.jupiter.api.^extension.ExtendWith
+import org.eclipse.xtext.testing.extensions.InjectionExtension
+import org.junit.jupiter.api.Test
+import static org.junit.jupiter.api.Assertions.assertTrue 
 
 @InjectWith(CheckInjectorProvider)
-@RunWith(XtextRunner)
+@ExtendWith(InjectionExtension)
 class IssueCodeValueTest extends AbstractCheckGenerationTestCase {
 
   static final String PACKAGE_NAME = "mypackage"
@@ -96,7 +97,7 @@ class IssueCodeValueTest extends AbstractCheckGenerationTestCase {
 
     for (issueCode: expectedIssueCodeValues.entrySet) {
       val expectedIssueCodeAssignment = '''public static final String «issueCode.key» = "«PACKAGE_NAME».«CATALOG_NAME»«ISSUE_CODES_SUFFIX».«issueCode.value»";'''
-      assertTrue('''«issueCodesClassName» contains correct initialization of «issueCode.key»''', issueCodesClass.contains(expectedIssueCodeAssignment))
+      assertTrue(issueCodesClass.contains(expectedIssueCodeAssignment), '''«issueCodesClassName» contains correct initialization of «issueCode.key»''')
     }
   }
 
diff --git a/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/core/test/AbstractCheckGenerationTestCase.java b/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/core/test/AbstractCheckGenerationTestCase.java
index 566394cacc..aca59bac33 100644
--- a/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/core/test/AbstractCheckGenerationTestCase.java
+++ b/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/core/test/AbstractCheckGenerationTestCase.java
@@ -11,6 +11,10 @@
 
 package com.avaloq.tools.ddk.check.core.test;
 
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.junit.jupiter.api.Assertions.fail;
+
 import java.io.IOException;
 import java.io.InputStream;
 import java.util.Collections;
@@ -76,7 +80,7 @@ public List<JavaSource> generateAndCompile(final InputStream sourceStream) {
       fail("Could not load test resource" + e.getMessage());
     }
     CheckCatalog root = (CheckCatalog) res.getContents().get(0);
-    assertNotNull("Resource should contain a CheckCatalog", root);
+    assertNotNull(root, "Resource should contain a CheckCatalog");
     // We also should have some Jvm model here.
     JvmType type = null;
     for (EObject obj : res.getContents()) {
@@ -85,7 +89,7 @@ public List<JavaSource> generateAndCompile(final InputStream sourceStream) {
         break;
       }
     }
-    assertNotNull("Should have an inferred Jvm model", type);
+    assertNotNull(type, "Should have an inferred Jvm model");
     // Run the generator using an in-memory file system access
     InMemoryFileSystemAccess fsa = new InMemoryFileSystemAccess();
     for (OutputConfiguration output : outputConfigurationProvider.getOutputConfigurations()) {
@@ -107,7 +111,7 @@ public List<JavaSource> generateAndCompile(final InputStream sourceStream) {
       final InMemoryJavaCompiler.Result result = javaCompiler.compile(sources.toArray(new JavaSource[sources.size()]));
       // Due to https://bugs.eclipse.org/bugs/show_bug.cgi?id=541225 we must ignore this warning here
       if (result.getCompilationProblems().stream().anyMatch(p -> "Pb(1102) At least one of the problems in category 'nls' is not analysed due to a compiler option being ignored".equals(p.getMessage()))) {
-        assertTrue("All sources should have been compiled without errors " + result.getCompilationProblems(), result.getCompilationProblems().isEmpty());
+        assertTrue(result.getCompilationProblems().isEmpty(), "All sources should have been compiled without errors " + result.getCompilationProblems());
       }
 
       return sources;
diff --git a/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/core/test/AbstractCheckTestCase.java b/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/core/test/AbstractCheckTestCase.java
index 63458ad54e..21ac794f36 100644
--- a/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/core/test/AbstractCheckTestCase.java
+++ b/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/core/test/AbstractCheckTestCase.java
@@ -11,6 +11,9 @@
 package com.avaloq.tools.ddk.check.core.test;
 
 import static com.google.common.collect.Sets.newHashSet;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.fail;
 
 import java.io.IOException;
 import java.io.InputStream;
@@ -38,9 +41,9 @@
 import org.eclipse.xtext.resource.XtextResourceSet;
 import org.eclipse.xtext.ui.testing.util.IResourcesSetupUtil;
 import org.eclipse.xtext.util.StringInputStream;
-import org.junit.AfterClass;
-import org.junit.Before;
-import org.junit.BeforeClass;
+import org.junit.jupiter.api.AfterAll;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.BeforeEach;
 
 import com.avaloq.tools.ddk.check.CheckConstants;
 import com.avaloq.tools.ddk.check.ui.internal.CheckActivator;
@@ -54,14 +57,12 @@
 import com.google.inject.Injector;
 import com.google.inject.Provider;
 
-import junit.framework.TestCase;
-
 
 /**
  * An abstract test class for tests on Check models. Allows creating a project and adding files.
  */
 @SuppressWarnings({"PMD.SignatureDeclareThrowsException", "restriction", "nls"})
-public abstract class AbstractCheckTestCase extends TestCase {
+public abstract class AbstractCheckTestCase {
   private static final int TWO_KILO_BYTES = 2048;
   protected static final Logger LOGGER = LogManager.getLogger(AbstractCheckTestCase.class);
   private static final PluginTestProjectManager PROJECT_MANAGER = new PluginTestProjectManager(CheckActivator.getInstance().getInjector(CheckConstants.GRAMMAR));
@@ -71,8 +72,7 @@ public abstract class AbstractCheckTestCase extends TestCase {
   @Inject
   private Provider<XtextResourceSet> resourceSetProvider;
 
-  @Override
-  @Before
+  @BeforeEach
   public void setUp() throws Exception {
     getInjector().injectMembers(this);
   }
@@ -83,7 +83,7 @@ public void setUp() throws Exception {
    * @throws Exception
    *           the exception
    */
-  @BeforeClass
+  @BeforeAll
   public static void prepareWorkspace() throws Exception {
     PROJECT_MANAGER.setup(ImmutableList.<TestSource> of());
   }
@@ -117,7 +117,7 @@ public <T> T get(final Class<T> clazz) {
   /**
    * Clean up after all tests have terminated.
    */
-  @AfterClass
+  @AfterAll
   public static void cleanUp() {
     PROJECT_MANAGER.teardown();
   }
@@ -215,7 +215,7 @@ public EObject getModel(final String fileName, final String content) throws Exce
     IFile file = createFile(fileName, content);
     Resource resource = get(XtextResourceSet.class).createResource(uri(file));
     resource.load(new StringInputStream(content), null);
-    assertEquals(resource.getErrors().toString(), 0, resource.getErrors().size());
+    assertEquals(0, resource.getErrors().size(), resource.getErrors().toString());
     return resource.getContents().get(0);
   }
 
@@ -264,7 +264,7 @@ public EObject getModel(final String fileName) throws Exception { // NOPMD
         }
       }
     }
-    assertEquals(resource.getErrors().toString(), 0, resource.getErrors().size());
+    assertEquals(0, resource.getErrors().size(), resource.getErrors().toString());
     return resource.getContents().get(0);
   }
 
@@ -293,7 +293,7 @@ public boolean apply(final IFile input) {
    */
   protected IProject getOrCreatePluginProject() throws CoreException {
     IWorkspaceRoot workspaceRoot = EcorePlugin.getWorkspaceRoot();
-    assertNotNull("No workspace; project cannot be created or found", workspaceRoot);
+    assertNotNull(workspaceRoot, "No workspace; project cannot be created or found");
     IProject project = workspaceRoot.getProject(PluginTestProjectManager.TEST_PROJECT_NAME);
     if (!project.exists()) {
       try {
@@ -349,7 +349,7 @@ protected void execute(final IProgressMonitor monitor) throws CoreException, Inv
     } catch (InterruptedException e) {
       fail("Error adding files to workspace: " + e.getMessage());
     }
-    assertEquals("All files successfully added to workspace", sourceFileNames.size(), getFiles().size());
+    assertEquals(sourceFileNames.size(), getFiles().size(), "All files successfully added to workspace");
   }
 
   /**
diff --git a/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/core/test/BasicModelTest.xtend b/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/core/test/BasicModelTest.xtend
index 1f0d2ade7f..42aad415be 100644
--- a/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/core/test/BasicModelTest.xtend
+++ b/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/core/test/BasicModelTest.xtend
@@ -4,7 +4,7 @@
  * are made available under the terms of the Eclipse Public License v1.0
  * which accompanies this distribution, and is available at
  * http://www.eclipse.org/legal/epl-v10.html
- *
+ * 
  * Contributors:
  *     Avaloq Group AG - initial API and implementation
  *******************************************************************************/
@@ -19,16 +19,15 @@ import com.avaloq.tools.ddk.check.core.test.util.CheckTestUtil
 import com.google.inject.Inject
 import org.eclipse.xtext.resource.XtextResource
 import org.eclipse.xtext.testing.InjectWith
-import org.eclipse.xtext.testing.XtextRunner
 import org.eclipse.xtext.testing.util.ParseHelper
-import org.junit.Ignore
-import org.junit.Test
-import org.junit.runner.RunWith
-
-import static org.junit.Assert.*
+import org.junit.jupiter.api.Test
+import org.eclipse.xtext.testing.extensions.InjectionExtension
+import org.junit.jupiter.api.^extension.ExtendWith
+import static org.junit.jupiter.api.Assertions.*
+import org.junit.jupiter.api.Disabled
 
 @InjectWith(typeof(CheckUiInjectorProvider))
-@RunWith(typeof(XtextRunner))
+@ExtendWith(typeof(InjectionExtension))
 class BasicModelTest {
 
   @Inject
@@ -46,7 +45,7 @@ class BasicModelTest {
   @Test
   def void testCreateEmptyModelWithPackageReference() {
     val model = parser.parse("package p catalog c {}")
-    assertNotNull("CheckCatalog with EPackage reference successfully created", model);
+    assertNotNull(model, "CheckCatalog with EPackage reference successfully created")
   }
 
   /**
@@ -55,7 +54,7 @@ class BasicModelTest {
   @Test
   def void testCreateEmptyModelWithGrammarReference() {
     val model = parser.parse("package p catalog c for grammar com.avaloq.tools.ddk.check.Check {}")
-    assertNotNull("CheckCatalog with Grammar reference successfully created", model);
+    assertNotNull(model, "CheckCatalog with Grammar reference successfully created")
   }
 
   /* Tests that an XIssueExpression takes message parameters. */
@@ -74,10 +73,10 @@ class BasicModelTest {
 
   /* Tests that Checks documented with ML_COMMENTs have an inferred description field. */
   @Test
-  @Ignore("Fails because DocumentedImplCustom uses the null resource description provider to get the document provider")
+  @Disabled("Fails because DocumentedImplCustom uses the null resource description provider to get the document provider")
   def void testInferingOfDescription() {
     val check = util.getFirstInstanceOf(parser.parse(modelUtil.modelWithCheck), typeof(Check))
-    assertEquals("No documentation.", check.description)
+    assertEquals(check.description, "No documentation.")
   }
 
   /* Tests that Checks have an implicit name which matches the ID. */
@@ -85,28 +84,33 @@ class BasicModelTest {
   def void testCheckNameIDIsPresent() {
     val id = "CheckID"
     val check = util.getFirstInstanceOf(parser.parse(modelUtil.modelWithCheck(id)), typeof(Check))
-    assertEquals("Check name field matches ID field", check.id, check.name)
-    assertEquals("Check name field matches supplied ID", id, check.name)
+    assertEquals(check.id, check.name, "Check name field matches ID field")
+    assertEquals(id, check.name, "Check name field matches supplied ID")
   }
 
   /* Tests that Checks have an implicit name which matches the ID even when the ID is missing. */
   @Test
   def void testCheckNameIDIsMissing() {
     val check = util.getFirstInstanceOf(parser.parse(modelUtil.modelWithCheck("")), typeof(Check))
-    assertNull("Check name is null", check.name)
+    assertNull(check.name, "Check name is null")
   }
 
   /* Tests that multi- and single-line comments are parsed in a model. */
   @Test
   def void testCommentsInModelParse() {
     val model = parser.parse(modelUtil.modelWithComments)
-    assertFalse("Syntax errors not expected but occurred", (model.eResource as XtextResource).parseResult.hasSyntaxErrors)
+    assertFalse((model.eResource as XtextResource).parseResult.hasSyntaxErrors,
+      "Syntax errors not expected but occurred")
   }
 
   /* Tests that t.message is allowed, despite "message" being a keyword. */
   @Test
   def void testKeywordAsIdentifier() {
-    val model = parser.parse(modelUtil.modelWithContext + "try { issue bind (\"mp0\", \"mp1\"); } catch (java.lang.Throwable t) { issue bind (t.message, \"foo\"); }" + "}}}}");
-    assertFalse("Syntax errors not expected but occurred", (model.eResource as XtextResource).parseResult.hasSyntaxErrors);
+    val model = parser.parse(
+      modelUtil.modelWithContext +
+        "try { issue bind (\"mp0\", \"mp1\"); } catch (java.lang.Throwable t) { issue bind (t.message, \"foo\"); }" +
+        "}}}}");
+    assertFalse((model.eResource as XtextResource).parseResult.hasSyntaxErrors,
+      "Syntax errors not expected but occurred")
   }
 }
diff --git a/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/core/test/BugAig1314.java b/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/core/test/BugAig1314.java
index a1d4ea748b..31394387ee 100644
--- a/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/core/test/BugAig1314.java
+++ b/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/core/test/BugAig1314.java
@@ -10,9 +10,9 @@
  *******************************************************************************/
 package com.avaloq.tools.ddk.check.core.test;
 
-import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.assertFalse;
-import static org.junit.Assert.assertTrue;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import java.io.InputStream;
 import java.net.MalformedURLException;
@@ -25,9 +25,9 @@
 import org.eclipse.xtext.resource.XtextResourceSet;
 import org.eclipse.xtext.scoping.IScope;
 import org.eclipse.xtext.testing.InjectWith;
-import org.eclipse.xtext.testing.XtextRunner;
-import org.junit.Test;
-import org.junit.runner.RunWith;
+import org.eclipse.xtext.testing.extensions.InjectionExtension;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
 
 import com.avaloq.tools.ddk.check.CheckInjectorProvider;
 import com.avaloq.tools.ddk.check.runtime.configuration.IModelLocation;
@@ -39,10 +39,10 @@
 /**
  * Some tests for AIG-1314, testing that the CatalogFromExtensionPointScope does not make the resource set grow more than expected.
  */
-@RunWith(XtextRunner.class)
+@ExtendWith(InjectionExtension.class)
 @InjectWith(CheckInjectorProvider.class)
 @SuppressWarnings("nls")
-public class BugAig1314 {
+class BugAig1314 {
 
   /** Constructor of super class is protected... */
   private static class TestScope extends CatalogFromExtensionPointScope {
@@ -86,7 +86,7 @@ public InputStream getCatalogStream() {
    *          resource set to check.
    */
   private void assertResourceSetEmpty(final XtextResourceSet rs) {
-    assertTrue("ResourceSet should be empty", rs.getURIResourceMap().isEmpty() && rs.getResources().isEmpty());
+    assertTrue(rs.getURIResourceMap().isEmpty() && rs.getResources().isEmpty(), "ResourceSet should be empty");
   }
 
   /**
@@ -100,12 +100,12 @@ private void assertResourceSetEmpty(final XtextResourceSet rs) {
    *          expected number of resources in the resource map
    */
   private void assertResourceSet(final XtextResourceSet rs, final int expected, final int inMap) {
-    assertTrue("Test wrong: must expect more than zero resources", expected > 0 && inMap > 0);
-    assertEquals("ResourceSet should not grow", expected, rs.getResources().size());
-    assertEquals("ResourceSet map size", inMap, rs.getURIResourceMap().size());
+    assertTrue(expected > 0 && inMap > 0, "Test wrong: must expect more than zero resources");
+    assertEquals(expected, rs.getResources().size(), "ResourceSet should not grow");
+    assertEquals(inMap, rs.getURIResourceMap().size(), "ResourceSet map size");
     for (Resource r : rs.getResources()) {
       URI uri = r.getURI();
-      assertTrue(uri.toString() + " not found in ResourceSet map", rs.getURIResourceMap().containsKey(uri));
+      assertTrue(rs.getURIResourceMap().containsKey(uri), uri.toString() + " not found in ResourceSet map");
     }
   }
 
@@ -116,14 +116,14 @@ private void assertResourceSet(final XtextResourceSet rs, final int expected, fi
    *          to check
    */
   private void assertIterableNotEmpty(final Iterable<?> iterable) {
-    assertFalse("Iterable should not be empty", Iterables.isEmpty(iterable));
+    assertFalse(Iterables.isEmpty(iterable), "Iterable should not be empty");
   }
 
   /**
    * Tests that querying the same scope twice doesn't make the resource set grow.
    */
   @Test
-  public void testSameScopeUseTwice() throws MalformedURLException, URISyntaxException {
+  void testSameScopeUseTwice() throws MalformedURLException, URISyntaxException {
     XtextResourceSet rs = new XtextResourceSet();
     URL url = createURL();
     ModelLocation modelLocation = createModelLocation(url);
@@ -142,7 +142,7 @@ public void testSameScopeUseTwice() throws MalformedURLException, URISyntaxExcep
    * Tests that querying two different scopes doesn't make the resource set grow. That one was the real cause of bug AIG-1314.
    */
   @Test
-  public void testDifferentScopeUseTwice() throws MalformedURLException, URISyntaxException {
+  void testDifferentScopeUseTwice() throws MalformedURLException, URISyntaxException {
     XtextResourceSet rs = new XtextResourceSet();
     URL url = createURL();
     ModelLocation modelLocation = createModelLocation(url);
diff --git a/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/core/test/BugAig830.xtend b/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/core/test/BugAig830.xtend
index e5c57fde49..854dace54c 100644
--- a/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/core/test/BugAig830.xtend
+++ b/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/core/test/BugAig830.xtend
@@ -16,15 +16,15 @@ import com.avaloq.tools.ddk.check.check.XIssueExpression
 import com.google.inject.Inject
 import org.eclipse.xtext.EcoreUtil2
 import org.eclipse.xtext.testing.InjectWith
-import org.eclipse.xtext.testing.XtextRunner
 import org.eclipse.xtext.testing.util.ParseHelper
 import org.eclipse.xtext.xbase.XbasePackage
-import org.junit.Assert
-import org.junit.Test
-import org.junit.runner.RunWith
+import org.eclipse.xtext.testing.extensions.InjectionExtension
+import org.junit.jupiter.api.^extension.ExtendWith
+import org.junit.jupiter.api.Test
+import static org.junit.jupiter.api.Assertions.*
 
 @InjectWith(typeof(CheckUiInjectorProvider))
-@RunWith(typeof(XtextRunner))
+@ExtendWith(typeof(InjectionExtension))
 class BugAig830 {
 
   @Inject
@@ -48,9 +48,9 @@ class BugAig830 {
   def void bugAig830() {
     val model = parser.parse(getModel())
     val issue = EcoreUtil2::getAllContentsOfType(model, typeof(XIssueExpression)).get(0)
-    Assert::assertNotNull(issue.markerFeature)
-    Assert::assertFalse(issue.markerFeature.eIsProxy)
-    Assert::assertEquals(XbasePackage.Literals::XVARIABLE_DECLARATION, issue.markerFeature.EContainingClass)
+    assertNotNull(issue.markerFeature)
+    assertFalse(issue.markerFeature.eIsProxy)
+    assertEquals(XbasePackage.Literals::XVARIABLE_DECLARATION, issue.markerFeature.EContainingClass)
   }
 
 }
diff --git a/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/core/test/BugDsl27.java b/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/core/test/BugDsl27.java
index c6ce548252..3d5e7973ce 100644
--- a/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/core/test/BugDsl27.java
+++ b/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/core/test/BugDsl27.java
@@ -14,9 +14,9 @@
 import java.io.InputStream;
 
 import org.eclipse.xtext.testing.InjectWith;
-import org.eclipse.xtext.testing.XtextRunner;
-import org.junit.Test;
-import org.junit.runner.RunWith;
+import org.eclipse.xtext.testing.extensions.InjectionExtension;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
 
 import com.avaloq.tools.ddk.check.CheckInjectorProvider;
 
@@ -25,15 +25,15 @@
  * Tests that the java code generated from BugDsl27 has no errors.
  */
 @InjectWith(CheckInjectorProvider.class)
-@RunWith(XtextRunner.class)
+@ExtendWith(InjectionExtension.class)
 @SuppressWarnings("nls")
-public class BugDsl27 extends AbstractCheckGenerationTestCase {
+class BugDsl27 extends AbstractCheckGenerationTestCase {
 
   /**
    * Tests that our test source compiles fine.
    */
   @Test
-  public void testGeneratedCodeHasNoErrors() {
+  void testGeneratedCodeHasNoErrors() {
     try (InputStream sourceStream = BugDsl27.class.getResourceAsStream("bugdsl27/BugDsl27")) {
       generateAndCompile(sourceStream);
     } catch (IOException exception) {
diff --git a/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/core/test/CheckScopingTest.xtend b/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/core/test/CheckScopingTest.xtend
index 7433dd6418..3c031610bb 100644
--- a/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/core/test/CheckScopingTest.xtend
+++ b/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/core/test/CheckScopingTest.xtend
@@ -4,7 +4,7 @@
  * are made available under the terms of the Eclipse Public License v1.0
  * which accompanies this distribution, and is available at
  * http://www.eclipse.org/legal/epl-v10.html
- *
+ * 
  * Contributors:
  *     Avaloq Group AG - initial API and implementation
  *******************************************************************************/
@@ -20,13 +20,14 @@ import com.google.common.collect.Lists
 import com.google.inject.Inject
 import java.util.List
 import org.eclipse.xtext.testing.InjectWith
-import org.eclipse.xtext.testing.XtextRunner
 import org.eclipse.xtext.ui.testing.util.IResourcesSetupUtil
-import org.junit.Test
-import org.junit.runner.RunWith
+import org.junit.jupiter.api.^extension.ExtendWith
+import org.eclipse.xtext.testing.extensions.InjectionExtension
+import org.junit.jupiter.api.Test
+import static org.junit.jupiter.api.Assertions.*
 
 @InjectWith(typeof(CheckUiInjectorProvider))
-@RunWith(typeof(XtextRunner))
+@ExtendWith(typeof(InjectionExtension))
 class CheckScopingTest extends AbstractCheckTestCase {
 
   @Inject CheckTestUtil util
@@ -61,10 +62,10 @@ class CheckScopingTest extends AbstractCheckTestCase {
     val model = getModel("CommonChecks") as CheckCatalog
 
     val illegalRefImpl = util.getFirstInstanceOf(model, typeof(Implementation))
-    val issueExpr      = util.getFirstInstanceOf(illegalRefImpl, typeof(XIssueExpression))
+    val issueExpr = util.getFirstInstanceOf(illegalRefImpl, typeof(XIssueExpression))
 
-    assertTrue("Referenced check cannot be resolved", issueExpr.check.eIsProxy)
-    assertNull("Referenced check name is null", issueExpr.check.name)
+    assertTrue(issueExpr.check.eIsProxy, "Referenced check cannot be resolved")
+    assertNull(issueExpr.check.name, "Referenced check name is null")
   }
 
   /*
@@ -75,6 +76,6 @@ class CheckScopingTest extends AbstractCheckTestCase {
   def void testCheckDescriptionIsInferred() {
     initializeTestProject
     val check = util.getFirstInstanceOf(getModel("CommonChecks"), typeof(Check))
-    assertEquals("Referenced check cannot be resolved", "This check is javadoc-like commented.", check.description)
+    assertEquals(check.description, "Referenced check cannot be resolved", "This check is javadoc-like commented.")
   }
 }
diff --git a/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/core/test/IssueCodeToLabelMapGenerationTest.xtend b/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/core/test/IssueCodeToLabelMapGenerationTest.xtend
index c5b381b555..b0c7826fdf 100644
--- a/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/core/test/IssueCodeToLabelMapGenerationTest.xtend
+++ b/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/core/test/IssueCodeToLabelMapGenerationTest.xtend
@@ -14,17 +14,18 @@ package com.avaloq.tools.ddk.check.core.test
 import com.avaloq.tools.ddk.check.CheckInjectorProvider
 import java.io.ByteArrayInputStream
 import org.eclipse.xtext.testing.InjectWith
-import org.eclipse.xtext.testing.XtextRunner
-import org.junit.Test
-import org.junit.runner.RunWith
 import java.util.List
 import org.eclipse.xtext.xbase.testing.JavaSource
+import org.junit.jupiter.api.^extension.ExtendWith
+import org.eclipse.xtext.testing.extensions.InjectionExtension
+import org.junit.jupiter.api.Test
+import static org.junit.jupiter.api.Assertions.*
 
 /**
  * Unit test for autogeneration of check issue code to label map.
  */
 @InjectWith(CheckInjectorProvider)
-@RunWith(XtextRunner)
+@ExtendWith(typeof(InjectionExtension))
 class IssueCodeToLabelMapGenerationTest extends AbstractCheckGenerationTestCase {
 
   static final String PACKAGE_NAME = "mypackage"
@@ -121,7 +122,7 @@ class IssueCodeToLabelMapGenerationTest extends AbstractCheckGenerationTestCase
     val catalogClass = compiledClassesList.findFirst[s | s.fileName.equals(catalogClassName)].code;
 
     for (code: expectedCatalog) {
-      assertTrue('''«catalogClassName» was generated correctly''', catalogClass.replaceAll("\\s+","").contains(code))
+      assertTrue( catalogClass.replaceAll("\\s+","").contains(code), '''«catalogClassName» was generated correctly''')
     }
   }
 
diff --git a/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/core/test/ProjectBasedTests.xtend b/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/core/test/ProjectBasedTests.xtend
index 10d3b47e0e..540d405e8c 100644
--- a/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/core/test/ProjectBasedTests.xtend
+++ b/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/core/test/ProjectBasedTests.xtend
@@ -19,13 +19,14 @@ import org.eclipse.core.resources.IMarker
 import org.eclipse.core.resources.IProject
 import org.eclipse.core.resources.IResource
 import org.eclipse.xtext.testing.InjectWith
-import org.eclipse.xtext.testing.XtextRunner
-import org.junit.Test
-import org.junit.runner.RunWith
 import org.eclipse.xtext.ui.testing.util.IResourcesSetupUtil
+import org.junit.jupiter.api.^extension.ExtendWith
+import org.eclipse.xtext.testing.extensions.InjectionExtension
+import org.junit.jupiter.api.Test
+import static org.junit.jupiter.api.Assertions.*
 
 @InjectWith(typeof(CheckUiInjectorProvider))
-@RunWith(typeof(XtextRunner))
+@ExtendWith(typeof(InjectionExtension))
 class ProjectBasedTests extends AbstractCheckTestCase {
 
   boolean initialized;
@@ -65,9 +66,9 @@ class ProjectBasedTests extends AbstractCheckTestCase {
     val IProject project = getOrCreatePluginProject()
     val IFile file = project.getFile(fileName);
     // enumerateContents(project);
-    assertTrue("Generated file should exist", file.exists);
-    assertFalse("Generated file should not be empty", isEmpty(file));
-    assertTrue("Generated file should not have errors", file.findMaxProblemSeverity(null, true, IResource::DEPTH_INFINITE) < IMarker::SEVERITY_ERROR);
+    assertTrue( file.exists,"Generated file should exist")
+    assertFalse( isEmpty(file),"Generated file should not be empty")
+    assertTrue( file.findMaxProblemSeverity(null, true, IResource::DEPTH_INFINITE) < IMarker::SEVERITY_ERROR,"Generated file should not have errors")
 
   }
 
diff --git a/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/formatting/CheckFormattingTest.xtend b/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/formatting/CheckFormattingTest.xtend
index 4b7f8c0677..027a376929 100644
--- a/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/formatting/CheckFormattingTest.xtend
+++ b/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/formatting/CheckFormattingTest.xtend
@@ -16,13 +16,13 @@ import com.google.inject.Inject
 import org.eclipse.xtext.formatting2.FormatterPreferenceKeys
 import org.eclipse.xtext.preferences.MapBasedPreferenceValues
 import org.eclipse.xtext.testing.InjectWith
-import org.eclipse.xtext.testing.XtextRunner
 import org.eclipse.xtext.testing.formatter.FormatterTestHelper
-import org.junit.Test
-import org.junit.runner.RunWith
+import org.junit.jupiter.api.^extension.ExtendWith
+import org.eclipse.xtext.testing.extensions.InjectionExtension
+import org.junit.jupiter.api.Test
 
 @InjectWith(typeof(CheckUiInjectorProvider))
-@RunWith(typeof(XtextRunner))
+@ExtendWith(typeof(InjectionExtension))
 class CheckFormattingTest {
 
   @Inject
diff --git a/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/test/core/CheckCoreTestSuite.java b/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/test/core/CheckCoreTestSuite.java
index dd15402859..79371b1229 100644
--- a/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/test/core/CheckCoreTestSuite.java
+++ b/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/test/core/CheckCoreTestSuite.java
@@ -10,42 +10,21 @@
  *******************************************************************************/
 package com.avaloq.tools.ddk.check.test.core;
 
-import org.junit.runner.RunWith;
-import org.junit.runners.Suite;
-
-import com.avaloq.tools.ddk.check.core.generator.IssueCodeValueTest;
-import com.avaloq.tools.ddk.check.core.test.BasicModelTest;
-import com.avaloq.tools.ddk.check.core.test.BugAig1314;
-import com.avaloq.tools.ddk.check.core.test.BugAig830;
-import com.avaloq.tools.ddk.check.core.test.BugDsl27;
-import com.avaloq.tools.ddk.check.core.test.CheckScopingTest;
-import com.avaloq.tools.ddk.check.core.test.IssueCodeToLabelMapGenerationTest;
-import com.avaloq.tools.ddk.check.core.test.ProjectBasedTests;
-import com.avaloq.tools.ddk.check.formatting.CheckFormattingTest;
-import com.avaloq.tools.ddk.check.validation.CheckApiAccessValidationsTest;
-import com.avaloq.tools.ddk.check.validation.CheckJavaValidatorUtilTest;
-import com.avaloq.tools.ddk.check.validation.CheckValidationTest;
+import org.junit.platform.suite.api.SelectPackages;
+import org.junit.platform.suite.api.Suite;
 
 
 /**
- * Empty class serving only as holder for JUnit4 annotations.
+ * Junit5 version of test suites. does not implement the logic in our DiscerningSuite.
  */
-@RunWith(Suite.class)
-@Suite.SuiteClasses({
+@Suite
+@SelectPackages({
 // @Format-Off
-  BasicModelTest.class,
-  CheckScopingTest.class,
-  CheckValidationTest.class,
-  CheckJavaValidatorUtilTest.class,
-  CheckFormattingTest.class,
-  BugAig830.class,
-  BugAig1314.class,
-  BugDsl27.class,
-  ProjectBasedTests.class,
-  CheckApiAccessValidationsTest.class,
-  IssueCodeToLabelMapGenerationTest.class,
-  IssueCodeValueTest.class
-// @Format-On
+  "com.avaloq.tools.ddk.check.core.generator",
+  "com.avaloq.tools.ddk.check.core.test",
+  "com.avaloq.tools.ddk.check.formatting",
+  "com.avaloq.tools.ddk.check.validation"
+  // @Format-On
 })
 public class CheckCoreTestSuite {
 
diff --git a/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/validation/CheckApiAccessValidationsTest.xtend b/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/validation/CheckApiAccessValidationsTest.xtend
index 37f141b582..0c9f980703 100644
--- a/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/validation/CheckApiAccessValidationsTest.xtend
+++ b/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/validation/CheckApiAccessValidationsTest.xtend
@@ -10,18 +10,18 @@
 package com.avaloq.tools.ddk.check.validation
 
 import org.eclipse.xtext.testing.InjectWith
-import org.junit.runner.RunWith
-import org.eclipse.xtext.testing.XtextRunner
 import com.avaloq.tools.ddk.check.CheckUiInjectorProvider
-import org.junit.Test
 import com.google.inject.Inject
 import org.eclipse.xtext.testing.util.ParseHelper
 import com.avaloq.tools.ddk.check.check.CheckCatalog
 import org.eclipse.xtext.testing.validation.ValidationTestHelper
 import org.eclipse.xtext.xtype.XtypePackage
+import org.junit.jupiter.api.^extension.ExtendWith
+import org.eclipse.xtext.testing.extensions.InjectionExtension
+import org.junit.jupiter.api.Test
 
 @InjectWith(typeof(CheckUiInjectorProvider))
-@RunWith(typeof(XtextRunner))
+@ExtendWith(typeof(InjectionExtension))
 class CheckApiAccessValidationsTest{
 
   @Inject
diff --git a/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/validation/CheckJavaValidatorUtilTest.java b/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/validation/CheckJavaValidatorUtilTest.java
index 1e59ac3a23..b862f5788c 100644
--- a/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/validation/CheckJavaValidatorUtilTest.java
+++ b/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/validation/CheckJavaValidatorUtilTest.java
@@ -10,26 +10,26 @@
  *******************************************************************************/
 package com.avaloq.tools.ddk.check.validation;
 
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
 import org.eclipse.core.runtime.IStatus;
 import org.eclipse.xtext.testing.InjectWith;
-import org.eclipse.xtext.testing.XtextRunner;
-import org.junit.Test;
-import org.junit.runner.RunWith;
+import org.eclipse.xtext.testing.extensions.InjectionExtension;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
 
 import com.avaloq.tools.ddk.check.CheckUiInjectorProvider;
 import com.google.inject.Inject;
 
-import junit.framework.TestCase;
-
 
 /**
  * Tests for com.avaloq.tools.ddk.check.validation.CheckJavaValidatorUtil.
  */
 
 @InjectWith(CheckUiInjectorProvider.class)
-@RunWith(XtextRunner.class)
+@ExtendWith(InjectionExtension.class)
 @SuppressWarnings("nls")
-public class CheckJavaValidatorUtilTest extends TestCase {
+class CheckJavaValidatorUtilTest {
 
   // assertion messages.
   private static final String STARTS_WITH_LOWER_CASE = "starts with lower case";
@@ -65,23 +65,23 @@ public class CheckJavaValidatorUtilTest extends TestCase {
    * Tests checkProjectName. The given values are valid.
    */
   @Test
-  public void projectNameIsValid() {
-    assertTrue(QUALIFIED_NAME, util.checkProjectName("project.name").isOK());
-    assertTrue(NON_QUALIFIED_NAME, util.checkProjectName("projectname").isOK());
+  void projectNameIsValid() {
+    assertTrue(util.checkProjectName("project.name").isOK(), QUALIFIED_NAME);
+    assertTrue(util.checkProjectName("projectname").isOK(), NON_QUALIFIED_NAME);
   }
 
   /**
    * Tests checkProjectName. The given values are invalid.
    */
   @Test
-  public void projectNameIsInvalid() {
-    assertTrue(NAME_IS_EMPTY, util.checkProjectName(EMPTY_STRING).matches(IStatus.ERROR));
-    assertTrue(STARTS_WITH_UPPERCASE_LETTER, util.checkProjectName("Project.name").matches(IStatus.ERROR));
-    assertTrue(STARTS_WITH_ILLEGAL_CHARACTER_DOT, util.checkProjectName(".projectname").matches(IStatus.ERROR));
-    assertTrue(CONTAINS_ILLEGAL_CHARACTER_DOLLAR, util.checkCatalogName("client$project").matches(IStatus.ERROR));
-    assertTrue(CONTAINS_ILLEGAL_CHARACTER_WHITESPACE, util.checkProjectName("project.name ").matches(IStatus.ERROR));
-    assertTrue(CONTAINS_UPPERCASE_LETTER, util.checkProjectName("proJect.Name").matches(IStatus.ERROR));
-    assertTrue(CONTAINS_DOUBLE_DOT, util.checkProjectName("project..name").matches(IStatus.ERROR));
+  void projectNameIsInvalid() {
+    assertTrue(util.checkProjectName(EMPTY_STRING).matches(IStatus.ERROR), NAME_IS_EMPTY);
+    assertTrue(util.checkProjectName("Project.name").matches(IStatus.ERROR), STARTS_WITH_UPPERCASE_LETTER);
+    assertTrue(util.checkProjectName(".projectname").matches(IStatus.ERROR), STARTS_WITH_ILLEGAL_CHARACTER_DOT);
+    assertTrue(util.checkCatalogName("client$project").matches(IStatus.ERROR), CONTAINS_ILLEGAL_CHARACTER_DOLLAR);
+    assertTrue(util.checkProjectName("project.name ").matches(IStatus.ERROR), CONTAINS_ILLEGAL_CHARACTER_WHITESPACE);
+    assertTrue(util.checkProjectName("proJect.Name").matches(IStatus.ERROR), CONTAINS_UPPERCASE_LETTER);
+    assertTrue(util.checkProjectName("project..name").matches(IStatus.ERROR), CONTAINS_DOUBLE_DOT);
   }
 
   /**
@@ -89,9 +89,9 @@ public void projectNameIsInvalid() {
    */
 
   @Test
-  public void packageNameIsValid() {
-    assertTrue(QUALIFIED_NAME, util.checkPackageName("package.name").isOK());
-    assertTrue(NON_QUALIFIED_NAME, util.checkPackageName("packagename").isOK());
+  void packageNameIsValid() {
+    assertTrue(util.checkPackageName("package.name").isOK(), QUALIFIED_NAME);
+    assertTrue(util.checkPackageName("packagename").isOK(), NON_QUALIFIED_NAME);
   }
 
   /**
@@ -99,72 +99,72 @@ public void packageNameIsValid() {
    */
 
   @Test
-  public void packageNameIsInvalid() {
-    assertTrue(NAME_IS_EMPTY, util.checkPackageName(EMPTY_STRING).matches(IStatus.ERROR));
-    assertTrue(STARTS_WITH_UPPERCASE_LETTER, util.checkPackageName("Package.name").matches(IStatus.ERROR));
-    assertTrue(STARTS_WITH_ILLEGAL_CHARACTER_DOT, util.checkPackageName(".packagename").matches(IStatus.ERROR));
-    assertTrue(CONTAINS_ILLEGAL_CHARACTER_WHITESPACE, util.checkPackageName("packagename ").matches(IStatus.ERROR));
-    assertTrue(CONTAINS_ILLEGAL_CHARACTER_DOLLAR, util.checkCatalogName("client$package").matches(IStatus.ERROR));
-    assertTrue(CONTAINS_UPPERCASE_LETTER, util.checkPackageName("package.Name").matches(IStatus.ERROR));
-    assertTrue(CONTAINS_DOUBLE_DOT, util.checkPackageName("package..name").matches(IStatus.ERROR));
+  void packageNameIsInvalid() {
+    assertTrue(util.checkPackageName(EMPTY_STRING).matches(IStatus.ERROR), NAME_IS_EMPTY);
+    assertTrue(util.checkPackageName("Package.name").matches(IStatus.ERROR), STARTS_WITH_UPPERCASE_LETTER);
+    assertTrue(util.checkPackageName(".packagename").matches(IStatus.ERROR), STARTS_WITH_ILLEGAL_CHARACTER_DOT);
+    assertTrue(util.checkPackageName("packagename ").matches(IStatus.ERROR), CONTAINS_ILLEGAL_CHARACTER_WHITESPACE);
+    assertTrue(util.checkCatalogName("client$package").matches(IStatus.ERROR), CONTAINS_ILLEGAL_CHARACTER_DOLLAR);
+    assertTrue(util.checkPackageName("package.Name").matches(IStatus.ERROR), CONTAINS_UPPERCASE_LETTER);
+    assertTrue(util.checkPackageName("package..name").matches(IStatus.ERROR), CONTAINS_DOUBLE_DOT);
   }
 
   /**
    * Tests checkCatalogName. The given values are valid.
    */
   @Test
-  public void catalogNameIsValid() {
-    assertTrue(STARTS_WITH_UPPERCASE_LETTER, util.checkCatalogName("Catalogname").isOK());
-    assertTrue(STARTS_WITH_AND_CONTAINS_UPPERCASE_LETTERS, util.checkCatalogName("CatalogName").isOK());
+  void catalogNameIsValid() {
+    assertTrue(util.checkCatalogName("Catalogname").isOK(), STARTS_WITH_UPPERCASE_LETTER);
+    assertTrue(util.checkCatalogName("CatalogName").isOK(), STARTS_WITH_AND_CONTAINS_UPPERCASE_LETTERS);
   }
 
   /**
    * Tests checkCatalogName. The given values are invalid.
    */
   @Test
-  public void catalogNameIsInvalid() {
-    assertTrue(NAME_IS_EMPTY, util.checkCatalogName(EMPTY_STRING).matches(IStatus.ERROR));
-    assertTrue(QUALIFIED_NAME, util.checkCatalogName("Catalog.Name").matches(IStatus.ERROR));
-    assertTrue(CONTAINS_ILLEGAL_CHARACTER, util.checkCatalogName(",Catalogname").matches(IStatus.ERROR));
-    assertTrue(CONTAINS_ILLEGAL_CHARACTER_DOLLAR, util.checkCatalogName("Client$Catalog").matches(IStatus.ERROR));
+  void catalogNameIsInvalid() {
+    assertTrue(util.checkCatalogName(EMPTY_STRING).matches(IStatus.ERROR), NAME_IS_EMPTY);
+    assertTrue(util.checkCatalogName("Catalog.Name").matches(IStatus.ERROR), QUALIFIED_NAME);
+    assertTrue(util.checkCatalogName(",Catalogname").matches(IStatus.ERROR), CONTAINS_ILLEGAL_CHARACTER);
+    assertTrue(util.checkCatalogName("Client$Catalog").matches(IStatus.ERROR), CONTAINS_ILLEGAL_CHARACTER_DOLLAR);
   }
 
   /**
    * Tests checkCatalogName. The given values are discouraged.
    */
   @Test
-  public void catalogNameIsDiscouraged() {
-    assertTrue(STARTS_WITH_LOWER_CASE, util.checkCatalogName("catalogname").matches(IStatus.WARNING));
-    assertTrue(STARTS_WITH_AND_CONTAINS_UPPERCASE_LETTERS, util.checkCatalogName("catalogName").matches(IStatus.WARNING));
+  void catalogNameIsDiscouraged() {
+    assertTrue(util.checkCatalogName("catalogname").matches(IStatus.WARNING), STARTS_WITH_LOWER_CASE);
+    assertTrue(util.checkCatalogName("catalogName").matches(IStatus.WARNING), STARTS_WITH_AND_CONTAINS_UPPERCASE_LETTERS);
   }
 
   /**
    * Tests checkCheckName. The given values are valid.
    */
   @Test
-  public void checkNameIsValid() {
-    assertTrue(STARTS_WITH_UPPERCASE_LETTER, util.checkCheckName("Checkname").isOK());
-    assertTrue(STARTS_WITH_AND_CONTAINS_UPPERCASE_LETTERS, util.checkCheckName("CheckName").isOK());
+  void checkNameIsValid() {
+    assertTrue(util.checkCheckName("Checkname").isOK(), STARTS_WITH_UPPERCASE_LETTER);
+    assertTrue(util.checkCheckName("CheckName").isOK(), STARTS_WITH_AND_CONTAINS_UPPERCASE_LETTERS);
   }
 
   /**
    * Tests checkCheckName. The given values are invalid.
    */
   @Test
-  public void checkNameIsInvalid() {
-    assertTrue(NAME_IS_EMPTY, util.checkCheckName(EMPTY_STRING).matches(IStatus.ERROR));
-    assertTrue(QUALIFIED_NAME, util.checkCheckName("Check.name").matches(IStatus.ERROR));
-    assertTrue(CONTAINS_ILLEGAL_CHARACTER, util.checkCheckName(",checkname").matches(IStatus.ERROR));
-    assertTrue(CONTAINS_ILLEGAL_CHARACTER_DOLLAR, util.checkCatalogName("client$check").matches(IStatus.ERROR));
+  void checkNameIsInvalid() {
+    assertTrue(util.checkCheckName(EMPTY_STRING).matches(IStatus.ERROR), NAME_IS_EMPTY);
+    assertTrue(util.checkCheckName("Check.name").matches(IStatus.ERROR), QUALIFIED_NAME);
+    assertTrue(util.checkCheckName(",checkname").matches(IStatus.ERROR), CONTAINS_ILLEGAL_CHARACTER);
+    assertTrue(util.checkCatalogName("client$check").matches(IStatus.ERROR), CONTAINS_ILLEGAL_CHARACTER_DOLLAR);
   }
 
   /**
    * Tests checkCheckName. The given values are discouraged.
    */
   @Test
-  public void checkNameIsDiscouraged() {
-    assertTrue(STARTS_WITH_LOWER_CASE, util.checkCheckName("checkname").matches(IStatus.WARNING));
-    assertTrue(STARTS_WITH_AND_CONTAINS_UPPERCASE_LETTERS, util.checkCheckName("checkName").matches(IStatus.WARNING));
+  void checkNameIsDiscouraged() {
+    assertTrue(util.checkCheckName("checkname").matches(IStatus.WARNING), STARTS_WITH_LOWER_CASE);
+    assertTrue(util.checkCheckName("checkName").matches(IStatus.WARNING), STARTS_WITH_AND_CONTAINS_UPPERCASE_LETTERS);
 
   }
 
@@ -172,28 +172,28 @@ public void checkNameIsDiscouraged() {
    * Tests checkCategoryName. The given values are valid.
    */
   @Test
-  public void categoryNameIsValid() {
-    assertTrue(STARTS_WITH_UPPERCASE_LETTER, util.checkCategoryName("Categoryname").isOK());
-    assertTrue(STARTS_WITH_AND_CONTAINS_UPPERCASE_LETTERS, util.checkCategoryName("CategoryName").isOK());
+  void categoryNameIsValid() {
+    assertTrue(util.checkCategoryName("Categoryname").isOK(), STARTS_WITH_UPPERCASE_LETTER);
+    assertTrue(util.checkCategoryName("CategoryName").isOK(), STARTS_WITH_AND_CONTAINS_UPPERCASE_LETTERS);
   }
 
   /**
    * Tests checkCategoryName. The given values are invalid.
    */
   @Test
-  public void categoryNameIsInvalid() {
-    assertTrue(NAME_IS_EMPTY, util.checkCategoryName(EMPTY_STRING).matches(IStatus.ERROR));
-    assertTrue(QUALIFIED_NAME, util.checkCategoryName("Category.name").matches(IStatus.ERROR));
-    assertTrue(CONTAINS_ILLEGAL_CHARACTER, util.checkCategoryName("%categoryname").matches(IStatus.ERROR));
-    assertTrue(CONTAINS_ILLEGAL_CHARACTER_DOLLAR, util.checkCatalogName("Client$Category").matches(IStatus.ERROR));
+  void categoryNameIsInvalid() {
+    assertTrue(util.checkCategoryName(EMPTY_STRING).matches(IStatus.ERROR), NAME_IS_EMPTY);
+    assertTrue(util.checkCategoryName("Category.name").matches(IStatus.ERROR), QUALIFIED_NAME);
+    assertTrue(util.checkCategoryName("%categoryname").matches(IStatus.ERROR), CONTAINS_ILLEGAL_CHARACTER);
+    assertTrue(util.checkCatalogName("Client$Category").matches(IStatus.ERROR), CONTAINS_ILLEGAL_CHARACTER_DOLLAR);
   }
 
   /**
    * Tests checkCategoryName. The given values are discouraged.
    */
   @Test
-  public void categoryNameIsDiscouraged() {
-    assertTrue(STARTS_WITH_LOWER_CASE, util.checkCategoryName("categoryname").matches(IStatus.WARNING));
-    assertTrue(STARTS_WITH_AND_CONTAINS_UPPERCASE_LETTERS, util.checkCategoryName("categoryName").matches(IStatus.WARNING));
+  void categoryNameIsDiscouraged() {
+    assertTrue(util.checkCategoryName("categoryname").matches(IStatus.WARNING), STARTS_WITH_LOWER_CASE);
+    assertTrue(util.checkCategoryName("categoryName").matches(IStatus.WARNING), STARTS_WITH_AND_CONTAINS_UPPERCASE_LETTERS);
   }
 }
diff --git a/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/validation/CheckValidationTest.xtend b/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/validation/CheckValidationTest.xtend
index 340eb56c36..42420211ec 100644
--- a/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/validation/CheckValidationTest.xtend
+++ b/com.avaloq.tools.ddk.check.core.test/src/com/avaloq/tools/ddk/check/validation/CheckValidationTest.xtend
@@ -16,15 +16,15 @@ import com.avaloq.tools.ddk.check.core.test.util.CheckModelUtil
 import com.google.common.collect.Lists
 import com.google.inject.Inject
 import org.eclipse.xtext.testing.InjectWith
-import org.eclipse.xtext.testing.XtextRunner
 import org.eclipse.xtext.testing.util.ParseHelper
 import org.eclipse.xtext.testing.validation.ValidationTestHelper
 import org.eclipse.xtext.xbase.XbasePackage$Literals
-import org.junit.Ignore
-import org.junit.Test
-import org.junit.runner.RunWith
 import com.avaloq.tools.ddk.check.validation.IssueCodes
 import com.avaloq.tools.ddk.check.check.CheckPackage
+import org.junit.jupiter.api.^extension.ExtendWith
+import org.eclipse.xtext.testing.extensions.InjectionExtension
+import org.junit.jupiter.api.Test
+import org.junit.jupiter.api.Disabled
 
 /*
  * Tests for various check validations as implemented in the validation classes
@@ -34,7 +34,7 @@ import com.avaloq.tools.ddk.check.check.CheckPackage
  * </ul>
  */
 @InjectWith(typeof(CheckUiInjectorProvider))
-@RunWith(typeof(XtextRunner))
+@ExtendWith(typeof(InjectionExtension))
 class CheckValidationTest {
 
   @Inject
@@ -97,7 +97,7 @@ class CheckValidationTest {
 
   /* Tests checkContextTypeIsUnique(Check) */
   @Test
-  @Ignore("Tests do not work because of scoping issues at run-time")
+  @Disabled("Tests do not work because of scoping issues at run-time")
   def void testContextTypeIsUnique() {
     // should fail
     var contexts = Lists::newArrayList("for C c {issue}", "for C d {issue}")
diff --git a/com.avaloq.tools.ddk.check.test.runtime.tests/src/com/avaloq/tools/ddk/check/test/runtime/CheckConfigurationIsAppliedTest.xtend b/com.avaloq.tools.ddk.check.test.runtime.tests/src/com/avaloq/tools/ddk/check/test/runtime/CheckConfigurationIsAppliedTest.xtend
index 5e7b6983e4..c27822ac24 100644
--- a/com.avaloq.tools.ddk.check.test.runtime.tests/src/com/avaloq/tools/ddk/check/test/runtime/CheckConfigurationIsAppliedTest.xtend
+++ b/com.avaloq.tools.ddk.check.test.runtime.tests/src/com/avaloq/tools/ddk/check/test/runtime/CheckConfigurationIsAppliedTest.xtend
@@ -20,14 +20,14 @@ import com.google.common.collect.Lists
 import com.google.inject.Inject
 import java.util.List
 import org.eclipse.xtext.testing.InjectWith
-import org.eclipse.xtext.testing.XtextRunner
 import org.eclipse.xtext.testing.validation.ValidationTestHelper
 import org.eclipse.xtext.ui.testing.util.IResourcesSetupUtil
-import org.junit.Test
-import org.junit.runner.RunWith
+import org.junit.jupiter.api.Test
+import org.eclipse.xtext.testing.extensions.InjectionExtension
+import org.junit.jupiter.api.^extension.ExtendWith
 
 @InjectWith(typeof(TestLanguageUiInjectorProvider))
-@RunWith(typeof(XtextRunner))
+@ExtendWith(typeof(InjectionExtension))
 class CheckConfigurationIsAppliedTest extends AbstractCheckTestCase {
 
   @Inject
diff --git a/com.avaloq.tools.ddk.check.test.runtime.tests/src/com/avaloq/tools/ddk/check/test/runtime/CheckExecutionEnvironmentProjectTest.xtend b/com.avaloq.tools.ddk.check.test.runtime.tests/src/com/avaloq/tools/ddk/check/test/runtime/CheckExecutionEnvironmentProjectTest.xtend
index 97ee56ff3e..bd0bff2858 100644
--- a/com.avaloq.tools.ddk.check.test.runtime.tests/src/com/avaloq/tools/ddk/check/test/runtime/CheckExecutionEnvironmentProjectTest.xtend
+++ b/com.avaloq.tools.ddk.check.test.runtime.tests/src/com/avaloq/tools/ddk/check/test/runtime/CheckExecutionEnvironmentProjectTest.xtend
@@ -19,14 +19,15 @@ import com.avaloq.tools.ddk.check.validation.ExecutionEnvironmentIssueCodes
 import com.avaloq.tools.ddk.check.validation.LibraryChecksIssueCodes
 import com.google.inject.Inject
 import org.eclipse.xtext.testing.InjectWith
-import org.eclipse.xtext.testing.XtextRunner
 import org.eclipse.xtext.testing.util.ParseHelper
 import org.eclipse.xtext.testing.validation.ValidationTestHelper
-import org.junit.Test
-import org.junit.runner.RunWith
+import org.junit.jupiter.api.^extension.ExtendWith
+import org.eclipse.xtext.testing.extensions.InjectionExtension
+import org.junit.jupiter.api.Test
+
 
 @InjectWith(typeof(TestLanguageUiInjectorProvider))
-@RunWith(typeof(XtextRunner))
+@ExtendWith(typeof(InjectionExtension))
 class CheckExecutionEnvironmentProjectTest extends AbstractCheckTestCase {
 
   @Inject
diff --git a/com.avaloq.tools.ddk.check.ui.test/src/com/avaloq/tools/ddk/check/ui/test/contentassist/AbstractCheckContentAssistBugTest.java b/com.avaloq.tools.ddk.check.ui.test/src/com/avaloq/tools/ddk/check/ui/test/contentassist/AbstractCheckContentAssistBugTest.java
index 73c7ff5ace..10b0719128 100644
--- a/com.avaloq.tools.ddk.check.ui.test/src/com/avaloq/tools/ddk/check/ui/test/contentassist/AbstractCheckContentAssistBugTest.java
+++ b/com.avaloq.tools.ddk.check.ui.test/src/com/avaloq/tools/ddk/check/ui/test/contentassist/AbstractCheckContentAssistBugTest.java
@@ -11,6 +11,7 @@
 package com.avaloq.tools.ddk.check.ui.test.contentassist;
 
 import static org.eclipse.xtext.ui.testing.util.JavaProjectSetupUtil.findJavaProject;
+import static org.junit.Assert.fail;
 
 import java.io.InputStream;
 
diff --git a/com.avaloq.tools.ddk.sample.helloworld.ui.test/META-INF/MANIFEST.MF b/com.avaloq.tools.ddk.sample.helloworld.ui.test/META-INF/MANIFEST.MF
index 96fc9d5955..6905750b8c 100644
--- a/com.avaloq.tools.ddk.sample.helloworld.ui.test/META-INF/MANIFEST.MF
+++ b/com.avaloq.tools.ddk.sample.helloworld.ui.test/META-INF/MANIFEST.MF
@@ -18,7 +18,10 @@ Require-Bundle: com.avaloq.tools.ddk.sample.helloworld,
  com.avaloq.tools.ddk.check.runtime.core,
  com.avaloq.tools.ddk.check.runtime.ui,
  com.avaloq.tools.ddk.check.core.test,
- org.eclipse.xtext.xbase.ui.testing
+ org.eclipse.xtext.xbase.ui.testing,
+ junit-jupiter-api,
+ junit-jupiter-engine,
+ junit-vintage-engine
 Bundle-RequiredExecutionEnvironment: JavaSE-21
 Export-Package: com.avaloq.tools.ddk.sample.helloworld.test,
  com.avaloq.tools.ddk.sample.helloworld.ui;x-internal=true
diff --git a/com.avaloq.tools.ddk.sample.helloworld.ui.test/src/com/avaloq/tools/ddk/sample/helloworld/check/CheckConfigurationIsAppliedTest.xtend b/com.avaloq.tools.ddk.sample.helloworld.ui.test/src/com/avaloq/tools/ddk/sample/helloworld/check/CheckConfigurationIsAppliedTest.xtend
index 7a4f8e9b6b..60376ba251 100644
--- a/com.avaloq.tools.ddk.sample.helloworld.ui.test/src/com/avaloq/tools/ddk/sample/helloworld/check/CheckConfigurationIsAppliedTest.xtend
+++ b/com.avaloq.tools.ddk.sample.helloworld.ui.test/src/com/avaloq/tools/ddk/sample/helloworld/check/CheckConfigurationIsAppliedTest.xtend
@@ -15,19 +15,19 @@ import com.google.common.collect.Lists
 import com.google.inject.Inject
 import java.util.List
 import org.eclipse.xtext.testing.InjectWith
-import org.eclipse.xtext.testing.XtextRunner
 import org.eclipse.xtext.testing.validation.ValidationTestHelper
 import org.eclipse.xtext.ui.testing.util.IResourcesSetupUtil
-import org.junit.Test
-import org.junit.runner.RunWith
 import com.avaloq.tools.ddk.sample.helloworld.helloWorld.Model
 import com.avaloq.tools.ddk.sample.helloworld.ui.internal.HelloworldActivator
 import com.avaloq.tools.ddk.sample.helloworld.helloWorld.HelloWorldPackage
 import com.avaloq.tools.ddk.sample.helloworld.validation.ExecutionEnvironmentIssueCodes
 import com.avaloq.tools.ddk.sample.helloworld.ui.HelloWorldUiInjectorProvider
+import org.junit.jupiter.api.^extension.ExtendWith
+import org.eclipse.xtext.testing.extensions.InjectionExtension
+import org.junit.jupiter.api.Test
 
 @InjectWith(typeof(HelloWorldUiInjectorProvider))
-@RunWith(XtextRunner)
+@ExtendWith(typeof(InjectionExtension))
 class CheckConfigurationIsAppliedTest extends AbstractCheckTestCase {
 
   @Inject
diff --git a/com.avaloq.tools.ddk.sample.helloworld.ui.test/src/com/avaloq/tools/ddk/sample/helloworld/check/CheckExecutionEnvironmentProjectTest.xtend b/com.avaloq.tools.ddk.sample.helloworld.ui.test/src/com/avaloq/tools/ddk/sample/helloworld/check/CheckExecutionEnvironmentProjectTest.xtend
index 6ee7691b4f..e3df63d53d 100644
--- a/com.avaloq.tools.ddk.sample.helloworld.ui.test/src/com/avaloq/tools/ddk/sample/helloworld/check/CheckExecutionEnvironmentProjectTest.xtend
+++ b/com.avaloq.tools.ddk.sample.helloworld.ui.test/src/com/avaloq/tools/ddk/sample/helloworld/check/CheckExecutionEnvironmentProjectTest.xtend
@@ -13,11 +13,12 @@ package com.avaloq.tools.ddk.sample.helloworld.check
 import com.avaloq.tools.ddk.check.core.test.AbstractCheckTestCase
 import com.google.inject.Inject
 import org.eclipse.xtext.testing.InjectWith
-import org.eclipse.xtext.testing.XtextRunner
 import org.eclipse.xtext.testing.util.ParseHelper
 import org.eclipse.xtext.testing.validation.ValidationTestHelper
-import org.junit.Test
-import org.junit.runner.RunWith
+import org.junit.jupiter.api.^extension.ExtendWith
+import org.eclipse.xtext.testing.extensions.InjectionExtension
+import org.junit.jupiter.api.Test
+
 import com.avaloq.tools.ddk.sample.helloworld.ui.internal.HelloworldActivator
 import com.avaloq.tools.ddk.sample.helloworld.helloWorld.Model
 import com.avaloq.tools.ddk.sample.helloworld.helloWorld.HelloWorldPackage
@@ -27,7 +28,7 @@ import com.avaloq.tools.ddk.sample.helloworld.validation.IssueCodes
 import com.avaloq.tools.ddk.sample.helloworld.ui.HelloWorldUiInjectorProvider
 
 @InjectWith(HelloWorldUiInjectorProvider)
-@RunWith(typeof(XtextRunner))
+@ExtendWith(typeof(InjectionExtension))
 class CheckExecutionEnvironmentProjectTest extends AbstractCheckTestCase {
 
   @Inject