Index: trunk/test/functional/org/openstreetmap/josm/tools/HttpClientTest.java
===================================================================
--- trunk/test/functional/org/openstreetmap/josm/tools/HttpClientTest.java	(revision 10222)
+++ trunk/test/functional/org/openstreetmap/josm/tools/HttpClientTest.java	(revision 10302)
@@ -101,4 +101,5 @@
                 .setHeader("Content-Type", "text/plain")
                 .setRequestBody(text.getBytes(StandardCharsets.UTF_8))
+                .setFinishOnCloseOutput(false) // to fix #12583, not sure if it's the best way to do it
                 .connect(progress);
         assertThat(response.getResponseCode(), is(200));
@@ -114,4 +115,5 @@
                 .setHeader("Content-Type", "text/plain")
                 .setRequestBody("".getBytes(StandardCharsets.UTF_8))
+                .setFinishOnCloseOutput(false) // to fix #12583, not sure if it's the best way to do it
                 .connect(progress);
         assertThat(response.getResponseCode(), is(200));