diff --git a/pytest-embedded/pytest_embedded/plugin.py b/pytest-embedded/pytest_embedded/plugin.py
index 70af0d45..d6c27029 100644
--- a/pytest-embedded/pytest_embedded/plugin.py
+++ b/pytest-embedded/pytest_embedded/plugin.py
@@ -1349,16 +1349,19 @@ def dut(
 @pytest.fixture
 def unity_tester(dut: t.Union['IdfDut', tuple['IdfDut']]) -> t.Optional['CaseTester']:
     try:
-        from pytest_embedded_idf import CaseTester, IdfDut
+        from pytest_embedded_idf import CaseTester
+        from pytest_embedded_idf.unity_tester import IdfUnityDutMixin
     except ImportError:
         yield None
     else:
-        # all dut instance must be IdfDut to use this fixture
-        for _dut in to_list(dut):
-            if not isinstance(_dut, IdfDut):
-                yield None
-
-        yield CaseTester(to_list(dut))
+        duts = to_list(dut)
+        # `CaseTester` drives the unity test menu, which every dut carrying
+        # `IdfUnityDutMixin` provides: `IdfDut` inherits it, and the dut factory
+        # mixes it into the qemu and esp-emu duts when the idf service is used.
+        if all(isinstance(_dut, IdfUnityDutMixin) for _dut in duts):
+            yield CaseTester(duts)
+        else:
+            yield None
 
 
 ##################
diff --git a/pytest-embedded/tests/test_base.py b/pytest-embedded/tests/test_base.py
index ede8d19c..361baaec 100644
--- a/pytest-embedded/tests/test_base.py
+++ b/pytest-embedded/tests/test_base.py
@@ -334,20 +334,27 @@ def test_expect_exact_no_matching_word_pass_rest(dut):
 def test_expect_from_timeout(testdir):
     testdir.makepyfile(r"""
         import threading
-        import time
         import pexpect
 
         def test_expect_from_timeout(msg_queue, dut):
+            stop = threading.Event()
+
             def write_bytes():
                 for _ in range(5):
+                    if stop.is_set():
+                        return
                     msg_queue.write('1')
-                    time.sleep(1.5)
+                    stop.wait(1.5)
 
             write_thread = threading.Thread(target=write_bytes, daemon=True)
             write_thread.start()
 
-            res = dut.expect(pexpect.TIMEOUT, timeout=4)
-            assert res == b'111'
+            try:
+                res = dut.expect(pexpect.TIMEOUT, timeout=4)
+                assert res == b'111'
+            finally:
+                stop.set()
+                write_thread.join(timeout=2)
     """)
 
     result = testdir.runpytest('-s')