Index: trunk/test/unit/org/openstreetmap/josm/gui/dialogs/validator/ValidatorTreePanelTest.java
===================================================================
--- trunk/test/unit/org/openstreetmap/josm/gui/dialogs/validator/ValidatorTreePanelTest.java	(revision 9811)
+++ trunk/test/unit/org/openstreetmap/josm/gui/dialogs/validator/ValidatorTreePanelTest.java	(revision 9811)
@@ -0,0 +1,66 @@
+// License: GPL. For details, see LICENSE file.
+package org.openstreetmap.josm.gui.dialogs.validator;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertNull;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.HashSet;
+import java.util.Set;
+
+import org.junit.BeforeClass;
+import org.junit.Test;
+import org.openstreetmap.josm.JOSMFixture;
+import org.openstreetmap.josm.data.osm.Node;
+import org.openstreetmap.josm.data.osm.OsmPrimitive;
+import org.openstreetmap.josm.data.validation.Severity;
+import org.openstreetmap.josm.data.validation.TestError;
+
+/**
+ * Unit tests of {@link ValidatorTreePanel} class.
+ */
+public class ValidatorTreePanelTest {
+
+    /**
+     * Setup tests
+     */
+    @BeforeClass
+    public static void setUpBeforeClass() {
+        JOSMFixture.createUnitTestFixture().init(true);
+    }
+
+    /**
+     * Unit test of {@link ValidatorTreePanel#ValidatorTreePanel}.
+     */
+    @Test
+    public void testValidatorTreePanel() {
+        assertNotNull(new ValidatorTreePanel());
+
+        ValidatorTreePanel vtp = new ValidatorTreePanel(new ArrayList<>(Arrays.asList(
+                new TestError(null, Severity.ERROR, "err", 0, new Node(1)),
+                new TestError(null, Severity.WARNING, "warn", 0, new Node(2)))));
+        assertNotNull(vtp);
+        assertEquals(1, vtp.getUpdateCount());
+        assertEquals(2, vtp.getErrors().size());
+        vtp.setVisible(true);
+        vtp.setVisible(false);
+        Node n = new Node(10);
+        vtp.setErrors(Arrays.asList(new TestError(null, Severity.ERROR, "", 0, n)));
+        assertEquals(1, vtp.getErrors().size());
+        vtp.selectRelatedErrors(Collections.<OsmPrimitive>singleton(n));
+        vtp.expandAll();
+        assertNotNull(vtp.getRoot());
+        vtp.resetErrors();
+        Set<? extends OsmPrimitive> filter = new HashSet<>(Arrays.asList(n));
+        vtp.setFilter(filter);
+        assertEquals(filter, vtp.getFilter());
+        vtp.setFilter(new HashSet<OsmPrimitive>());
+        assertNull(vtp.getFilter());
+        vtp.setFilter(null);
+        assertNull(vtp.getFilter());
+        vtp.destroy();
+    }
+}