Index: trunk/test/unit/org/openstreetmap/josm/actions/SelectSharedChildObjectsActionTest.java
===================================================================
--- trunk/test/unit/org/openstreetmap/josm/actions/SelectSharedChildObjectsActionTest.java	(revision 18814)
+++ trunk/test/unit/org/openstreetmap/josm/actions/SelectSharedChildObjectsActionTest.java	(revision 18814)
@@ -0,0 +1,70 @@
+// License: GPL. For details, see LICENSE file.
+package org.openstreetmap.josm.actions;
+
+import static org.junit.jupiter.api.Assertions.assertAll;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertSame;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.openstreetmap.josm.TestUtils;
+import org.openstreetmap.josm.data.osm.DataSet;
+import org.openstreetmap.josm.data.osm.Way;
+import org.openstreetmap.josm.gui.MainApplication;
+import org.openstreetmap.josm.gui.layer.OsmDataLayer;
+
+/**
+ * Test class for {@link SelectSharedChildObjectsAction}
+ */
+class SelectSharedChildObjectsActionTest {
+    private static SelectSharedChildObjectsAction action;
+    private DataSet ds;
+
+    @BeforeAll
+    static void classSetup() {
+        action = new SelectSharedChildObjectsAction();
+    }
+
+    @BeforeEach
+    void setup() {
+        ds = new DataSet();
+        MainApplication.getLayerManager().addLayer(new OsmDataLayer(ds, "SelectSharedChildObjectsActionTest", null));
+    }
+
+    @Test
+    void testNoIntersection() {
+        Way way1 = TestUtils.newWay("", TestUtils.newNode(""), TestUtils.newNode(""), TestUtils.newNode(""));
+        Way way2 = TestUtils.newWay("", TestUtils.newNode(""), TestUtils.newNode(""), TestUtils.newNode(""));
+        ds.addPrimitiveRecursive(way1);
+        ds.addPrimitiveRecursive(way2);
+        ds.setSelected(way1, way2);
+        assertAll("Sanity check that the current selection code works before we check the selection action",
+                () -> assertEquals(2, ds.getSelected().size()),
+                () -> assertTrue(ds.getSelected().contains(way1)),
+                () -> assertTrue(ds.getSelected().contains(way2)));
+
+        action.actionPerformed(null);
+        assertEquals(0, ds.getSelected().size(), "Nothing should be selected");
+    }
+
+    @Test
+    void testBasicIntersection() {
+        Way way1 = TestUtils.newWay("", TestUtils.newNode(""), TestUtils.newNode(""), TestUtils.newNode(""));
+        Way way2 = TestUtils.newWay("", TestUtils.newNode(""), TestUtils.newNode(""));
+        ds.addPrimitiveRecursive(way1);
+        ds.addPrimitiveRecursive(way2);
+        way2.addNode(1, way1.getNode(1));
+        ds.setSelected(way1, way2);
+        assertAll("Sanity check that the current selection code works before we check the selection action",
+                () -> assertEquals(2, ds.getSelected().size()),
+                () -> assertTrue(ds.getSelected().contains(way1)),
+                () -> assertTrue(ds.getSelected().contains(way2)));
+
+        action.actionPerformed(null);
+        assertAll("Check that the selected object is the common node",
+                () -> assertEquals(1, ds.getSelected().size()),
+                () -> assertSame(way1.getNode(1), ds.getSelected().iterator().next()));
+    }
+}