diff -r 000000000000 -r 6474c204b198 toolkit/devtools/server/tests/unit/test_reattach-thread.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/toolkit/devtools/server/tests/unit/test_reattach-thread.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,58 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+/**
+ * Test that reattaching to a previously detached thread works.
+ */
+
+var gClient, gDebuggee, gThreadClient, gTabClient;
+
+function run_test()
+{
+  initTestDebuggerServer();
+  gDebuggee = testGlobal("test-reattach");
+  DebuggerServer.addTestGlobal(gDebuggee);
+
+  let transport = DebuggerServer.connectPipe();
+  gClient = new DebuggerClient(transport);
+  gClient.connect(() => {
+    attachTestTab(gClient, "test-reattach", (aReply, aTabClient) => {
+      gTabClient = aTabClient;
+      test_attach();
+    });
+  });
+  do_test_pending();
+}
+
+function test_attach()
+{
+  gTabClient.attachThread({}, (aResponse, aThreadClient) => {
+    do_check_eq(aThreadClient.state, "paused");
+    gThreadClient = aThreadClient;
+    aThreadClient.resume(test_detach);
+  });
+}
+
+function test_detach()
+{
+  gThreadClient.detach(() => {
+    do_check_eq(gThreadClient.state, "detached");
+    do_check_eq(gTabClient.thread, null);
+    test_reattach();
+  });
+}
+
+function test_reattach()
+{
+  gTabClient.attachThread({}, (aResponse, aThreadClient) => {
+    do_check_neq(gThreadClient, aThreadClient);
+    do_check_eq(aThreadClient.state, "paused");
+    do_check_eq(gTabClient.thread, aThreadClient);
+    aThreadClient.resume(cleanup);
+  });
+}
+
+function cleanup()
+{
+  gClient.close(do_test_finished);
+}