Index: trunk/test/unit/org/openstreetmap/josm/actions/AlignInCircleActionTest.java
===================================================================
--- trunk/test/unit/org/openstreetmap/josm/actions/AlignInCircleActionTest.java	(revision 17386)
+++ trunk/test/unit/org/openstreetmap/josm/actions/AlignInCircleActionTest.java	(revision 17386)
@@ -0,0 +1,152 @@
+// License: GPL. For details, see LICENSE file.
+package org.openstreetmap.josm.actions;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import java.nio.file.Files;
+import java.nio.file.Paths;
+import java.util.Set;
+import java.util.stream.Collectors;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.RegisterExtension;
+import org.openstreetmap.josm.TestUtils;
+import org.openstreetmap.josm.command.Command;
+import org.openstreetmap.josm.data.osm.DataSet;
+import org.openstreetmap.josm.data.osm.Node;
+import org.openstreetmap.josm.data.osm.Way;
+import org.openstreetmap.josm.io.OsmReader;
+import org.openstreetmap.josm.testutils.JOSMTestRules;
+
+import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
+
+/**
+ * Unit tests for class {@link AlignInLineAction}.
+ */
+final class AlignInCircleActionTest {
+
+    /**
+     * Setup test.
+     */
+    @RegisterExtension
+    @SuppressFBWarnings(value = "URF_UNREAD_PUBLIC_OR_PROTECTED_FIELD")
+    public JOSMTestRules test = new JOSMTestRules().projection();
+
+
+    /**
+     * Test case: way with several nodes selected
+     * @throws Exception if an error occurs
+     */
+    @Test
+    void testWaySelected() throws Exception {
+        DataSet ds = OsmReader.parseDataSet(Files.newInputStream(Paths.get(TestUtils.getTestDataRoot(), "alignCircleBefore.osm")), null);
+        DataSet ds2 = OsmReader.parseDataSet(Files.newInputStream(Paths.get(TestUtils.getTestDataRoot(), "alignCircleAfter1.osm")), null);
+
+        Way roundabout = null;
+        for (Way w : ds.getWays()) {
+            if ("roundabout".equals(w.get("junction"))) {
+                roundabout = w;
+                break;
+            }
+        }
+        assertNotNull(roundabout);
+        if (roundabout != null) {
+            ds.setSelected(roundabout);
+            Command c = AlignInCircleAction.buildCommand(ds);
+            c.executeCommand();
+            Way expected = (Way) ds2.getPrimitiveById(roundabout);
+            assertNotNull(expected);
+            assertEquals(expected, roundabout);
+            assertEquals(expected.getNodesCount(), roundabout.getNodesCount());
+            for (Node n1 : roundabout.getNodes()) {
+                Node n2 = (Node) ds2.getPrimitiveById(n1);
+                assertEquals(n1.lat(), n2.lat(), 1e-5);
+                assertEquals(n1.lon(), n2.lon(), 1e-5);
+            }
+        }
+    }
+
+    /**
+     * Non-regression test for <a href="https://josm.openstreetmap.de/ticket/20041">Bug #20041</a>.
+     * Don't create move commands when no node is visibly moved
+     * @throws Exception if an error occurs
+     */
+    @Test
+    void testTicket20041() throws Exception {
+        DataSet ds = OsmReader.parseDataSet(Files.newInputStream(Paths.get(TestUtils.getTestDataRoot(), "alignCircleAfter1.osm")), null);
+
+        Way roundabout = null;
+        for (Way w : ds.getWays()) {
+            if ("roundabout".equals(w.get("junction"))) {
+                roundabout = w;
+                break;
+            }
+        }
+        assertNotNull(roundabout);
+        if (roundabout != null) {
+            ds.setSelected(roundabout);
+            assertThrows(AlignInCircleAction.InvalidSelection.class, () -> AlignInCircleAction.buildCommand(ds));
+        }
+    }
+
+    /**
+     * Test case: way with several nodes selected
+     * @throws Exception if an error occurs
+     */
+    @Test
+    void testNodesSelected() throws Exception {
+        DataSet ds = OsmReader.parseDataSet(Files.newInputStream(Paths.get(TestUtils.getTestDataRoot(), "alignCircleBefore.osm")), null);
+        DataSet ds2 = OsmReader.parseDataSet(Files.newInputStream(Paths.get(TestUtils.getTestDataRoot(), "alignCircleAfter2.osm")), null);
+
+        Way circularWay = null;
+        for (Way w : ds.getWays()) {
+            if ("roundabout".equals(w.get("junction"))) {
+                circularWay = w;
+                break;
+            }
+        }
+        assertNotNull(circularWay);
+        if (circularWay != null) {
+            ds.setSelected(circularWay.getNodes());
+            Command c = AlignInCircleAction.buildCommand(ds);
+            assertNotNull(c);
+            c.executeCommand();
+            Way expected = (Way) ds2.getPrimitiveById(circularWay);
+            assertNotNull(expected);
+            assertEquals(expected, circularWay);
+            assertEquals(expected.getNodesCount(), circularWay.getNodesCount());
+            for (Node n1 : circularWay.getNodes()) {
+                Node n2 = (Node) ds2.getPrimitiveById(n1);
+                assertEquals(n1.lat(), n2.lat(), 1e-5);
+                assertEquals(n1.lon(), n2.lon(), 1e-5);
+            }
+        }
+    }
+
+    /**
+     * Test case: original roundabout was split, two ways selected, they build a closed ring
+     * @throws Exception if an error occurs
+     */
+    @Test
+    void testOpenWaysSelected() throws Exception {
+        DataSet ds = OsmReader.parseDataSet(Files.newInputStream(Paths.get(TestUtils.getTestDataRoot(), "alignCircleTwoWaysBefore.osm")), null);
+        DataSet ds2 = OsmReader.parseDataSet(Files.newInputStream(Paths.get(TestUtils.getTestDataRoot(), "alignCircleTwoWaysAfter.osm")), null);
+
+        Set<Way> junctions = ds.getWays().stream().filter(w -> "roundabout".equals(w.get("junction"))).collect(Collectors.toSet());
+        assertEquals(2, junctions.size());
+        ds.setSelected(junctions);
+        Command c = AlignInCircleAction.buildCommand(ds);
+        assertNotNull(c);
+        c.executeCommand();
+        for (Way way : junctions) {
+            for (Node n1 : way.getNodes()) {
+                Node n2 = (Node) ds2.getPrimitiveById(n1);
+                assertEquals(n1.lat(), n2.lat(), 1e-5);
+                assertEquals(n1.lon(), n2.lon(), 1e-5);
+            }
+        }
+    }
+
+}