diff --git a/src/main/java/de/neemann/digital/cli/CommandLineTester.java b/src/main/java/de/neemann/digital/cli/CommandLineTester.java
index 9a718358a..55fab611a 100644
--- a/src/main/java/de/neemann/digital/cli/CommandLineTester.java
+++ b/src/main/java/de/neemann/digital/cli/CommandLineTester.java
@@ -10,11 +10,11 @@ import de.neemann.digital.cli.cli.BasicCommand;
 import de.neemann.digital.cli.cli.CLIException;
 import de.neemann.digital.core.ErrorDetector;
 import de.neemann.digital.core.Model;
+import de.neemann.digital.core.element.Keys;
 import de.neemann.digital.draw.elements.Circuit;
 import de.neemann.digital.draw.elements.VisualElement;
 import de.neemann.digital.lang.Lang;
 import de.neemann.digital.testing.TestCaseDescription;
-import de.neemann.digital.testing.TestCaseElement;
 import de.neemann.digital.testing.TestExecutor;
 
 import java.io.File;
@@ -59,7 +59,7 @@ public class CommandLineTester {
         ArrayList<TestCase> tsl = new ArrayList<>();
         for (VisualElement el : circuit.getTestCases())
             tsl.add(new TestCase(
-                    el.getElementAttributes().get(TestCaseElement.TESTDATA),
+                    el.getElementAttributes().get(Keys.TESTDATA),
                     el.getElementAttributes().getLabel()));
         return tsl;
     }
diff --git a/src/main/java/de/neemann/digital/core/element/Keys.java b/src/main/java/de/neemann/digital/core/element/Keys.java
index 869952ce3..9cceabaf3 100644
--- a/src/main/java/de/neemann/digital/core/element/Keys.java
+++ b/src/main/java/de/neemann/digital/core/element/Keys.java
@@ -20,6 +20,7 @@ import de.neemann.digital.draw.library.ElementLibrary;
 import de.neemann.digital.draw.model.InverterConfig;
 import de.neemann.digital.draw.shapes.CustomCircuitShapeType;
 import de.neemann.digital.draw.shapes.custom.CustomShapeDescription;
+import de.neemann.digital.testing.TestCaseDescription;
 import de.neemann.gui.Screen;
 import de.neemann.gui.language.Language;
 
@@ -869,4 +870,10 @@ public final class Keys {
     public static final Key<Boolean> MIRROR =
             new Key<>("mirror", false).allowGroupEdit().setSecondary();
 
+    /**
+     * The test data
+     */
+    public static final Key<TestCaseDescription> TESTDATA =
+            new Key<>("Testdata", () -> new TestCaseDescription(""));
+
 }
diff --git a/src/main/java/de/neemann/digital/gui/Main.java b/src/main/java/de/neemann/digital/gui/Main.java
index efc77d073..d38fe2ec6 100644
--- a/src/main/java/de/neemann/digital/gui/Main.java
+++ b/src/main/java/de/neemann/digital/gui/Main.java
@@ -54,7 +54,6 @@ import de.neemann.digital.hdl.printer.CodePrinter;
 import de.neemann.digital.hdl.verilog2.VerilogGenerator;
 import de.neemann.digital.hdl.vhdl2.VHDLGenerator;
 import de.neemann.digital.lang.Lang;
-import de.neemann.digital.testing.TestCaseElement;
 import de.neemann.digital.testing.TestingDataException;
 import de.neemann.digital.toolchain.Configuration;
 import de.neemann.digital.undo.ChangedListener;
@@ -1131,7 +1130,7 @@ public final class Main extends JFrame implements ClosingWindowListener.ConfirmS
             ArrayList<ValueTableDialog.TestSet> tsl = new ArrayList<>();
             for (VisualElement el : circuitComponent.getCircuit().getTestCases())
                 tsl.add(new ValueTableDialog.TestSet(
-                        el.getElementAttributes().get(TestCaseElement.TESTDATA),
+                        el.getElementAttributes().get(Keys.TESTDATA),
                         el.getElementAttributes().getLabel()));
 
             if (tsl.isEmpty())
diff --git a/src/main/java/de/neemann/digital/gui/components/testing/TestCaseDescriptionDialog.java b/src/main/java/de/neemann/digital/gui/components/testing/TestCaseDescriptionDialog.java
index d1179438e..70044becb 100644
--- a/src/main/java/de/neemann/digital/gui/components/testing/TestCaseDescriptionDialog.java
+++ b/src/main/java/de/neemann/digital/gui/components/testing/TestCaseDescriptionDialog.java
@@ -5,6 +5,7 @@
  */
 package de.neemann.digital.gui.components.testing;
 
+import de.neemann.digital.core.element.Keys;
 import de.neemann.digital.draw.elements.PinException;
 import de.neemann.digital.draw.elements.VisualElement;
 import de.neemann.digital.gui.Main;
@@ -14,7 +15,6 @@ import de.neemann.digital.gui.components.modification.ModifyAttribute;
 import de.neemann.digital.gui.components.table.ShowStringDialog;
 import de.neemann.digital.lang.Lang;
 import de.neemann.digital.testing.TestCaseDescription;
-import de.neemann.digital.testing.TestCaseElement;
 import de.neemann.digital.testing.Transitions;
 import de.neemann.digital.testing.parser.ParserException;
 import de.neemann.gui.ErrorMessage;
@@ -103,7 +103,7 @@ public class TestCaseDescriptionDialog extends JDialog {
                         data.setDataString(text.getText());
                         if (parent instanceof Main) {
                             CircuitComponent cc = ((Main) parent).getCircuitComponent();
-                            element.getElementAttributes().set(TestCaseElement.TESTDATA, data);
+                            element.getElementAttributes().set(Keys.TESTDATA, data);
                             cc.getMain().startTests();
                         }
                     } catch (ParserException | IOException e1) {
@@ -122,7 +122,7 @@ public class TestCaseDescriptionDialog extends JDialog {
                             && !initialDataString.equals(data.getDataString())
                             && parent instanceof Main) {
                         CircuitComponent cc = ((Main) parent).getCircuitComponent();
-                        cc.modify(new ModifyAttribute<>(element, TestCaseElement.TESTDATA, new TestCaseDescription(data)));
+                        cc.modify(new ModifyAttribute<>(element, Keys.TESTDATA, new TestCaseDescription(data)));
                     }
                     dispose();
                 } catch (ParserException | IOException e1) {
diff --git a/src/main/java/de/neemann/digital/hdl/verilog2/VerilogTestBenchCreator.java b/src/main/java/de/neemann/digital/hdl/verilog2/VerilogTestBenchCreator.java
index 795e4f620..d3d390c8e 100644
--- a/src/main/java/de/neemann/digital/hdl/verilog2/VerilogTestBenchCreator.java
+++ b/src/main/java/de/neemann/digital/hdl/verilog2/VerilogTestBenchCreator.java
@@ -28,7 +28,7 @@ import java.io.File;
 import java.io.IOException;
 import java.util.ArrayList;
 
-import static de.neemann.digital.testing.TestCaseElement.TESTDATA;
+import static de.neemann.digital.core.element.Keys.TESTDATA;
 
 import java.util.logging.Level;
 import java.util.logging.Logger;
diff --git a/src/main/java/de/neemann/digital/hdl/vhdl2/VHDLTestBenchCreator.java b/src/main/java/de/neemann/digital/hdl/vhdl2/VHDLTestBenchCreator.java
index 3b1b7d734..df0b058c0 100644
--- a/src/main/java/de/neemann/digital/hdl/vhdl2/VHDLTestBenchCreator.java
+++ b/src/main/java/de/neemann/digital/hdl/vhdl2/VHDLTestBenchCreator.java
@@ -26,7 +26,7 @@ import java.io.File;
 import java.io.IOException;
 import java.util.ArrayList;
 
-import static de.neemann.digital.testing.TestCaseElement.TESTDATA;
+import static de.neemann.digital.core.element.Keys.TESTDATA;
 
 /**
  * Creates a test bench for a model.
diff --git a/src/main/java/de/neemann/digital/testing/FolderTestRunner.java b/src/main/java/de/neemann/digital/testing/FolderTestRunner.java
index db9b43441..03b7f7b7c 100644
--- a/src/main/java/de/neemann/digital/testing/FolderTestRunner.java
+++ b/src/main/java/de/neemann/digital/testing/FolderTestRunner.java
@@ -7,6 +7,7 @@ package de.neemann.digital.testing;
 
 import de.neemann.digital.core.Model;
 import de.neemann.digital.core.NodeException;
+import de.neemann.digital.core.element.Keys;
 import de.neemann.digital.draw.elements.Circuit;
 import de.neemann.digital.draw.elements.PinException;
 import de.neemann.digital.draw.elements.VisualElement;
@@ -188,7 +189,7 @@ public class FolderTestRunner {
                     ArrayList<TestCase> testCases = new ArrayList<>();
                     for (VisualElement el : circuit.getTestCases()) {
                         String label = el.getElementAttributes().getLabel();
-                        TestCaseDescription testData = el.getElementAttributes().get(TestCaseElement.TESTDATA);
+                        TestCaseDescription testData = el.getElementAttributes().get(Keys.TESTDATA);
                         testCases.add(new TestCase(label, testData));
                     }
                     if (testCases.isEmpty()) {
diff --git a/src/main/java/de/neemann/digital/testing/TestCaseDescription.java b/src/main/java/de/neemann/digital/testing/TestCaseDescription.java
index 5270751c5..35e4ee235 100644
--- a/src/main/java/de/neemann/digital/testing/TestCaseDescription.java
+++ b/src/main/java/de/neemann/digital/testing/TestCaseDescription.java
@@ -106,4 +106,9 @@ public class TestCaseDescription {
     public int hashCode() {
         return dataString != null ? dataString.hashCode() : 0;
     }
+
+    @Override
+    public String toString() {
+        return dataString;
+    }
 }
diff --git a/src/main/java/de/neemann/digital/testing/TestCaseElement.java b/src/main/java/de/neemann/digital/testing/TestCaseElement.java
index 1106ea7f9..084d12782 100644
--- a/src/main/java/de/neemann/digital/testing/TestCaseElement.java
+++ b/src/main/java/de/neemann/digital/testing/TestCaseElement.java
@@ -15,18 +15,13 @@ import de.neemann.digital.core.element.*;
  */
 public class TestCaseElement implements Element {
 
-    /**
-     * the used {@link ElementAttributes} key
-     */
-    public static final Key<TestCaseDescription> TESTDATA = new Key<>("Testdata", () -> new TestCaseDescription(""));
-
     /**
      * The TestCaseElement description
      */
     public static final ElementTypeDescription TESTCASEDESCRIPTION
             = new ElementTypeDescription("Testcase", TestCaseElement.class)
             .addAttribute(Keys.LABEL)
-            .addAttribute(TESTDATA)
+            .addAttribute(Keys.TESTDATA)
             .addAttribute(Keys.ENABLED)
             .supportsHDL();
 
diff --git a/src/test/java/de/neemann/digital/draw/library/JarComponentManagerTest.java b/src/test/java/de/neemann/digital/draw/library/JarComponentManagerTest.java
index e4d40c690..163f961e3 100644
--- a/src/test/java/de/neemann/digital/draw/library/JarComponentManagerTest.java
+++ b/src/test/java/de/neemann/digital/draw/library/JarComponentManagerTest.java
@@ -5,6 +5,7 @@
  */
 package de.neemann.digital.draw.library;
 
+import de.neemann.digital.core.element.Keys;
 import de.neemann.digital.draw.elements.VisualElement;
 import de.neemann.digital.integration.Resources;
 import de.neemann.digital.integration.ToBreakRunner;
@@ -37,7 +38,7 @@ public class JarComponentManagerTest extends TestCase {
 
         for (VisualElement ve : br.getCircuit().getElements()) {
             if (ve.equalsDescription(TestCaseElement.TESTCASEDESCRIPTION)) {
-                TestCaseDescription td = ve.getElementAttributes().get(TestCaseElement.TESTDATA);
+                TestCaseDescription td = ve.getElementAttributes().get(Keys.TESTDATA);
                 TestExecutor tr = new TestExecutor(td).create(br.getModel());
                 assertTrue(tr.allPassed());
             }
diff --git a/src/test/java/de/neemann/digital/hdl/hgs/ParserTest.java b/src/test/java/de/neemann/digital/hdl/hgs/ParserTest.java
index 669151e18..e9a3bdb0b 100644
--- a/src/test/java/de/neemann/digital/hdl/hgs/ParserTest.java
+++ b/src/test/java/de/neemann/digital/hdl/hgs/ParserTest.java
@@ -375,6 +375,19 @@ public class ParserTest extends TestCase {
         assertEquals("false;", c.toString());
     }
 
+    public void testStringCreation() throws IOException, ParserException, HGSEvalException {
+        String code = "?>Test:<? print(n); str:=output();";
+        Statement s = new Parser(code).parse(false);
+
+        Context c = new Context().declareVar("n", 3);
+        s.execute(c);
+        assertEquals("Test:3", c.getVar("str"));
+
+        c = new Context().declareVar("n", 12);
+        s.execute(c);
+        assertEquals("Test:12", c.getVar("str"));
+    }
+
     public void testAddFunction() throws IOException, ParserException, HGSEvalException {
         Statement s = new Parser("a : in <?=type(Bits)?>;").parse();
         Context funcs = new Context().declareVar("type", new Function(1) {
diff --git a/src/test/java/de/neemann/digital/integration/TestExamples.java b/src/test/java/de/neemann/digital/integration/TestExamples.java
index 2dc450077..d5d1e4e39 100644
--- a/src/test/java/de/neemann/digital/integration/TestExamples.java
+++ b/src/test/java/de/neemann/digital/integration/TestExamples.java
@@ -84,7 +84,7 @@ public class TestExamples extends TestCase {
                         testCasesInFiles++;
 
                         String label = el.getElementAttributes().getLabel();
-                        TestCaseDescription td = el.getElementAttributes().get(TestCaseElement.TESTDATA);
+                        TestCaseDescription td = el.getElementAttributes().get(Keys.TESTDATA);
 
                         Model model = new ModelCreator(br.getCircuit(), br.getLibrary()).createModel(false);
                         ErrorDetector ed = new ErrorDetector();
diff --git a/src/test/java/de/neemann/digital/integration/TestInGUI.java b/src/test/java/de/neemann/digital/integration/TestInGUI.java
index fa9958730..85724d126 100644
--- a/src/test/java/de/neemann/digital/integration/TestInGUI.java
+++ b/src/test/java/de/neemann/digital/integration/TestInGUI.java
@@ -61,7 +61,7 @@ import java.util.List;
 import static de.neemann.digital.draw.shapes.GenericShape.SIZE;
 import static de.neemann.digital.draw.shapes.GenericShape.SIZE2;
 import static de.neemann.digital.integration.GuiTester.getBaseContainer;
-import static de.neemann.digital.testing.TestCaseElement.TESTDATA;
+import static de.neemann.digital.core.element.Keys.TESTDATA;
 
 /**
  * These tests are excluded from the maven build because gui tests are sometimes fragile.