Improve unit test coverage for various core classes

Added and updated unit tests in `maven/core-unittests` to improve coverage for:
- `com.codename1.io.MalformedURLException`
- `com.codename1.ui.BrowserWindow$EvalRequest`
- `com.codename1.ui.BrowserComponent$JSExpression`
- `com.codename1.properties.UiBinding` (converters)
- `com.codename1.ui.events.ComponentStateChangeEvent`
- `com.codename1.charts.views.RangeStackedBarChart`
- `com.codename1.ui.plaf.CSSBorder` (RadialGradient logic)

The tests use `UITestBase` and `@FormTest` as per conventions.

Author: google-labs-jules[bot]

maven/core-unittests/src/test/java/com/codename1/charts/views/RangeStackedBarChartTest.java

@@ -0,0 +1,15 @@
+package com.codename1.charts.views;
+
+import com.codename1.junit.UITestBase;
+import com.codename1.junit.FormTest;
+import org.junit.jupiter.api.Assertions;
+
+public class RangeStackedBarChartTest extends UITestBase {
+
+    @FormTest
+    public void testGetChartType() {
+        RangeStackedBarChart chart = new RangeStackedBarChart();
+        Assertions.assertEquals("RangeStackedBar", chart.getChartType());
+    }
+
+}

maven/core-unittests/src/test/java/com/codename1/io/MalformedURLExceptionTest.java

@@ -0,0 +1,20 @@
+package com.codename1.io;
+
+import com.codename1.ui.Display;
+import com.codename1.junit.UITestBase;
+import com.codename1.junit.FormTest;
+import com.codename1.testing.TestCodenameOneImplementation;
+import org.junit.jupiter.api.Assertions;
+
+public class MalformedURLExceptionTest extends UITestBase {
+
+    @FormTest
+    public void testMalformedURLException() {
+        MalformedURLException ex = new MalformedURLException();
+        Assertions.assertNull(ex.getMessage());
+
+        ex = new MalformedURLException("Test Message");
+        Assertions.assertEquals("Test Message", ex.getMessage());
+    }
+
+}

maven/core-unittests/src/test/java/com/codename1/properties/UiBindingConvertersTest.java

@@ -0,0 +1,42 @@
+package com.codename1.properties;
+
+import com.codename1.junit.UITestBase;
+import com.codename1.junit.FormTest;
+import org.junit.jupiter.api.Assertions;
+
+public class UiBindingConvertersTest extends UITestBase {
+
+    @FormTest
+    public void testIntegerConverter() {
+        UiBinding.IntegerConverter converter = new UiBinding.IntegerConverter();
+        Assertions.assertNull(converter.convert(null));
+        Assertions.assertEquals(123, converter.convert(123));
+        Assertions.assertEquals(123, converter.convert("123"));
+        Assertions.assertEquals(123, converter.convert(123.45));
+    }
+
+    @FormTest
+    public void testLongConverter() {
+        UiBinding.LongConverter converter = new UiBinding.LongConverter();
+        Assertions.assertNull(converter.convert(null));
+        Assertions.assertEquals(123L, converter.convert(123L));
+        Assertions.assertEquals(123L, converter.convert("123"));
+        Assertions.assertEquals(123L, converter.convert(123.45));
+    }
+
+    @FormTest
+    public void testFloatConverter() {
+        UiBinding.FloatConverter converter = new UiBinding.FloatConverter();
+        Assertions.assertNull(converter.convert(null));
+        Assertions.assertEquals(123.45f, (Float) converter.convert(123.45f), 0.001f);
+        Assertions.assertEquals(123.45f, (Float) converter.convert("123.45"), 0.001f);
+    }
+
+    @FormTest
+    public void testDoubleConverter() {
+        UiBinding.DoubleConverter converter = new UiBinding.DoubleConverter();
+        Assertions.assertNull(converter.convert(null));
+        Assertions.assertEquals(123.45, (Double) converter.convert(123.45), 0.001);
+        Assertions.assertEquals(123.45, (Double) converter.convert("123.45"), 0.001);
+    }
+}

maven/core-unittests/src/test/java/com/codename1/ui/BrowserComponentTest.java

@@ -190,4 +190,10 @@ private static class DummyPeerComponent extends PeerComponent {
             s.setMargin(0, 0, 0, 0);
         }
     }
+
+    @FormTest
+    public void testJSExpression() {
+        BrowserComponent.JSExpression expression = new BrowserComponent.JSExpression("window.innerWidth");
+        assertEquals("window.innerWidth", expression.toString());
+    }
 }

maven/core-unittests/src/test/java/com/codename1/ui/BrowserWindowTest.java

@@ -59,4 +59,11 @@ public void actionPerformed(ActionEvent evt) {
         window.removeCloseListener(closeListener);
         assertFalse(implementation.getNativeBrowserWindowCloseListener().contains(closeListener));
     }
+
+    @FormTest
+    public void testEvalRequest() {
+        BrowserWindow.EvalRequest request = new BrowserWindow.EvalRequest();
+        request.setJS("alert('Hello');");
+        assertEquals("alert('Hello');", request.getJS());
+    }
 }

maven/core-unittests/src/test/java/com/codename1/ui/events/ComponentStateChangeEventTest.java

@@ -0,0 +1,23 @@
+package com.codename1.ui.events;
+
+import com.codename1.ui.Component;
+import com.codename1.ui.Container;
+import com.codename1.junit.UITestBase;
+import com.codename1.junit.FormTest;
+import org.junit.jupiter.api.Assertions;
+
+public class ComponentStateChangeEventTest extends UITestBase {
+
+    @FormTest
+    public void testComponentStateChangeEvent() {
+        Component cmp = new Container();
+        ComponentStateChangeEvent event = new ComponentStateChangeEvent(cmp, true);
+
+        Assertions.assertEquals(cmp, event.getSource());
+        Assertions.assertTrue(event.isInitialized());
+
+        event = new ComponentStateChangeEvent(cmp, false);
+        Assertions.assertFalse(event.isInitialized());
+    }
+
+}

maven/core-unittests/src/test/java/com/codename1/ui/plaf/CSSBorderTest.java

@@ -175,4 +175,42 @@ public void testBoxShadow() {
             border.toCSSString(); // BoxShadow toCSSString throws RuntimeException as per source
         });
     }
+
+    @FormTest
+    public void testRadialGradient() throws Exception {
+        // Use reflection to test RadialGradient
+        CSSBorder border = new CSSBorder((Resources)null);
+
+        // Reflection to create RadialGradient
+        Class<?> radialGradientClass = Class.forName("com.codename1.ui.plaf.CSSBorder$RadialGradient");
+        java.lang.reflect.Constructor<?> rgCtor = radialGradientClass.getDeclaredConstructor(CSSBorder.class);
+        rgCtor.setAccessible(true);
+        Object radialGradient = rgCtor.newInstance(border);
+
+        // Create BackgroundImage and attach RadialGradient
+        Class<?> bgImageClass = Class.forName("com.codename1.ui.plaf.CSSBorder$BackgroundImage");
+        java.lang.reflect.Constructor<?> bgCtor = bgImageClass.getDeclaredConstructor(CSSBorder.class);
+        bgCtor.setAccessible(true);
+        Object bgImage = bgCtor.newInstance(border);
+
+        java.lang.reflect.Field rgField = bgImageClass.getDeclaredField("radialGradient");
+        rgField.setAccessible(true);
+        rgField.set(bgImage, radialGradient);
+
+        // Attach BackgroundImage to CSSBorder
+        java.lang.reflect.Field bgImagesField = CSSBorder.class.getDeclaredField("backgroundImages");
+        bgImagesField.setAccessible(true);
+        Object bgImagesArray = java.lang.reflect.Array.newInstance(bgImageClass, 1);
+        java.lang.reflect.Array.set(bgImagesArray, 0, bgImage);
+        bgImagesField.set(border, bgImagesArray);
+
+        // Verify toCSSString
+        try {
+            border.toCSSString();
+            Assertions.fail("RadialGradient toCSSString should throw RuntimeException");
+        } catch(RuntimeException ex) {
+            // Expected
+            Assertions.assertEquals("RadialGradlient toCSSString() not implemented yet", ex.getMessage());
+        }
+    }
 }