diff --git a/tests/ingester/test_fs_source.py b/tests/ingester/test_fs_source.py
index 73c7cf34..31c7b838 100644
--- a/tests/ingester/test_fs_source.py
+++ b/tests/ingester/test_fs_source.py
@@ -307,12 +307,13 @@ async def test_fs_source_fetch_reads_off_event_loop_thread(fs_root: Path):
     """The file read and md5 are both proportional to file size and must run
     off the event-loop thread, or a large file would freeze every other
     worker's coroutine for the duration of the read. Capture the thread the
-    read+hash runs on and assert it is not the main thread."""
+    read+hash runs on and assert it is not the event-loop thread."""
     import threading
 
     src = FSSource(root=fs_root)
     target = fs_root / "a.md"
 
+    event_loop_thread = threading.current_thread()
     called_from: list[threading.Thread] = []
     original = src._read_body
 
@@ -320,12 +321,12 @@ async def test_fs_source_fetch_reads_off_event_loop_thread(fs_root: Path):
         called_from.append(threading.current_thread())
         return original(path, uri)
 
-    src._read_body = spy  # type: ignore[method-assign]
+    src._read_body = spy  # type: ignore[method-assign]  # ty: ignore[invalid-assignment]
 
     result = await src.fetch(target.as_uri())
     assert result.body == b"alpha"
     assert called_from, "_read_body was never called"
-    assert called_from[0] is not threading.main_thread(), (
+    assert called_from[0] is not event_loop_thread, (
         "FSSource._read_body ran on the event-loop thread; the read+hash must "
         "be dispatched via asyncio.to_thread"
     )
diff --git a/tests/test_chunker.py b/tests/test_chunker.py
index 9b897fc2..e59681a0 100644
--- a/tests/test_chunker.py
+++ b/tests/test_chunker.py
@@ -631,6 +631,7 @@ This is content.
         mock_client.get = AsyncMock(side_effect=[poll_resp, result_resp])
         mock_client_class.return_value.__aenter__.return_value = mock_client
 
+        event_loop_thread = threading.current_thread()
         called_from: list[threading.Thread] = []
 
         class FakeDoc:
@@ -642,7 +643,7 @@ This is content.
 
         assert len(chunks) == 1
         assert called_from, "model_dump_json was never called"
-        assert called_from[0] is not threading.main_thread(), (
+        assert called_from[0] is not event_loop_thread, (
             "DoclingDocument.model_dump_json ran on the event-loop thread; it "
             "must be dispatched via asyncio.to_thread"
         )
diff --git a/tests/test_converters.py b/tests/test_converters.py
index 916307e0..7447586d 100644
--- a/tests/test_converters.py
+++ b/tests/test_converters.py
@@ -108,21 +108,24 @@ async def test_parse_zip_runs_off_event_loop_thread():
     converter = get_converter(config)
     assert isinstance(converter, DoclingServeConverter)
 
-    converter.client.submit_and_poll_zip = AsyncMock(return_value=b"zip-bytes")
+    converter.client.submit_and_poll_zip = AsyncMock(  # ty: ignore[invalid-assignment]
+        return_value=b"zip-bytes"
+    )
 
+    event_loop_thread = threading.current_thread()
     called_from: list[threading.Thread] = []
 
     def spy(zip_bytes, name):
         called_from.append(threading.current_thread())
         return Mock()
 
-    converter._parse_zip_to_docling = spy  # type: ignore[method-assign]
+    converter._parse_zip_to_docling = spy  # type: ignore[method-assign]  # ty: ignore[invalid-assignment]
 
     files = {"files": ("doc.pdf", b"pdf", "application/octet-stream")}
     await converter._make_request(files, "doc.pdf")
 
     assert called_from, "_parse_zip_to_docling was never called"
-    assert called_from[0] is not threading.main_thread(), (
+    assert called_from[0] is not event_loop_thread, (
         "_parse_zip_to_docling ran on the event-loop thread; it must be "
         "dispatched via asyncio.to_thread"
     )
diff --git a/tests/test_pdf_attachments.py b/tests/test_pdf_attachments.py
index 702f855b..69851570 100644
--- a/tests/test_pdf_attachments.py
+++ b/tests/test_pdf_attachments.py
@@ -494,7 +494,8 @@ async def test_extract_pdf_attachments_called_off_event_loop_thread(
     duration of pdfium I/O, stalling every other concurrent worker.
 
     We verify this by capturing the thread identity inside a spy wrapper: if
-    asyncio.to_thread is used correctly the spy runs on a non-main thread."""
+    asyncio.to_thread is used correctly the spy runs off the event-loop thread."""
+    event_loop_thread = threading.current_thread()
     called_from: list[threading.Thread] = []
 
     def spy(body, uri, *, depth):
@@ -514,7 +515,7 @@ async def test_extract_pdf_attachments_called_off_event_loop_thread(
         await _reconcile_pdf_attachments(client, parent, pdf_bytes, depth=0)
 
     assert called_from, "_extract_pdf_attachments was never called"
-    assert called_from[0] is not threading.main_thread(), (
+    assert called_from[0] is not event_loop_thread, (
         "_extract_pdf_attachments ran on the event-loop thread; "
         "it must be dispatched via asyncio.to_thread to avoid blocking the loop"
     )
diff --git a/tests/test_pdf_split.py b/tests/test_pdf_split.py
index 7c253f9a..9ea00a8c 100644
--- a/tests/test_pdf_split.py
+++ b/tests/test_pdf_split.py
@@ -174,6 +174,7 @@ async def test_concatenate_runs_off_event_loop_thread(tmp_path, monkeypatch):
         async def convert_file(self, path: Path, *, source_uri):
             return DoclingDocument(name="slice")
 
+    event_loop_thread = threading.current_thread()
     called_from: list[threading.Thread] = []
 
     def spy(docs):
@@ -193,7 +194,7 @@ async def test_concatenate_runs_off_event_loop_thread(tmp_path, monkeypatch):
     )
 
     assert called_from, "concatenate was never called"
-    assert called_from[0] is not threading.main_thread(), (
+    assert called_from[0] is not event_loop_thread, (
         "DoclingDocument.concatenate ran on the event-loop thread; it must be "
         "dispatched via asyncio.to_thread"
     )