Index: trunk/test/unit/org/openstreetmap/josm/io/ChangesetQueryTest.java
===================================================================
--- trunk/test/unit/org/openstreetmap/josm/io/ChangesetQueryTest.java	(revision 17843)
+++ trunk/test/unit/org/openstreetmap/josm/io/ChangesetQueryTest.java	(revision 17843)
@@ -0,0 +1,51 @@
+// License: GPL. For details, see LICENSE file.
+package org.openstreetmap.josm.io;
+
+import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.RegisterExtension;
+import org.openstreetmap.josm.testutils.JOSMTestRules;
+
+import java.time.Instant;
+import java.util.Arrays;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+/**
+ * Unit tests of {@link ChangesetQuery}
+ */
+class ChangesetQueryTest {
+
+    /**
+     * Setup test.
+     */
+    @RegisterExtension
+    @SuppressFBWarnings(value = "URF_UNREAD_PUBLIC_OR_PROTECTED_FIELD")
+    public JOSMTestRules test = new JOSMTestRules().preferences();
+
+    /**
+     * Unit tests of {@link ChangesetQuery#getQueryString()}
+     */
+    @Test
+    void testQueryString() {
+        assertEquals("", new ChangesetQuery().getQueryString());
+        assertThrows(IllegalStateException.class, () -> ChangesetQuery.forCurrentUser().getQueryString());
+        assertEquals("display_name=foobar",
+                new ChangesetQuery().forUser("foobar").getQueryString());
+        assertEquals("user=4713",
+                new ChangesetQuery().forUser(4713).getQueryString());
+        assertEquals("time=1970-01-01T00:00:00Z",
+                new ChangesetQuery().closedAfter(Instant.EPOCH).getQueryString());
+        assertEquals("changesets=47,13",
+                new ChangesetQuery().forChangesetIds(Arrays.asList(47L, 13L)).getQueryString());
+        assertEquals("time=1971-02-02T16:22:18.368Z,1970-01-01T00:00:00Z",
+                new ChangesetQuery().closedAfterAndCreatedBefore(Instant.ofEpochMilli(1L << 35L), Instant.EPOCH).getQueryString());
+        assertEquals("bbox=12.0,34.0,56.0,78.0",
+                new ChangesetQuery().inBbox(12, 34, 56, 78).getQueryString());
+        assertEquals("closed=true",
+                new ChangesetQuery().beingClosed(true).getQueryString());
+        assertEquals("open=true",
+                new ChangesetQuery().beingOpen(true).getQueryString());
+    }
+}
Index: trunk/test/unit/org/openstreetmap/josm/io/ChangesetQueryUrlParserTest.java
===================================================================
--- trunk/test/unit/org/openstreetmap/josm/io/ChangesetQueryUrlParserTest.java	(revision 17841)
+++ trunk/test/unit/org/openstreetmap/josm/io/ChangesetQueryUrlParserTest.java	(revision 17843)
@@ -151,6 +151,5 @@
         assertNotNull(q);
         assertNotNull(q.getClosedAfter());
-        OffsetDateTime cal = q.getClosedAfter().toInstant().atOffset(ZoneOffset.UTC);
-        assertEquals(OffsetDateTime.of(2009, 12, 25, 10, 0, 0, 0, ZoneOffset.UTC), cal);
+        assertEquals(OffsetDateTime.of(2009, 12, 25, 10, 0, 0, 0, ZoneOffset.UTC).toInstant(), q.getClosedAfter());
 
         // OK