diff --git a/craft_cli/messages.py b/craft_cli/messages.py
index 8ed2549..c9b0293 100644
--- a/craft_cli/messages.py
+++ b/craft_cli/messages.py
@@ -70,6 +70,9 @@ class _MessageInfo:  # pylint: disable=too-many-instance-attributes
 # the size of bytes chunk that the pipe reader will read at once
 _PIPE_READER_CHUNK_SIZE = 4096
 
+# set to true when running *application* tests so some behaviours change
+TESTMODE = False
+
 
 def _get_terminal_width() -> int:
     """Return the number of columns of the terminal."""
@@ -193,13 +196,17 @@ def stop(self) -> None:
 
 
 class _Printer:
-    """Handle writing the different messages to the different outputs (out, err and log)."""
+    """Handle writing the different messages to the different outputs (out, err and log).
+
+    If TESTMODE is True, this class changes its behaviour: the spinner is never started,
+    so there is no thread polluting messages when running tests if they take too long to run.
+    """
 
     def __init__(self, log_filepath: pathlib.Path) -> None:
         # holder of the previous message
         self.prv_msg: Optional[_MessageInfo] = None
 
-        # the open log file (will be closed explicitly when the thread ends)
+        # open the log file (will be closed explicitly later)
         self.log = open(log_filepath, "wt", encoding="utf8")  # pylint: disable=consider-using-with
 
         # keep account of output streams with unfinished lines
@@ -207,7 +214,8 @@ def __init__(self, log_filepath: pathlib.Path) -> None:
 
         # run the spinner supervisor
         self.spinner = _Spinner(self)
-        self.spinner.start()
+        if not TESTMODE:
+            self.spinner.start()
 
     def _write_line(self, message: _MessageInfo, *, spintext: str = "") -> None:
         """Write a simple line message to the screen."""
@@ -366,7 +374,8 @@ def stop(self) -> None:
         - add a new line to the screen (if needed)
         - close the log file
         """
-        self.spinner.stop()
+        if not TESTMODE:
+            self.spinner.stop()
         if self.unfinished_stream is not None:
             print(flush=True, file=self.unfinished_stream)
         self.log.close()
diff --git a/tests/unit/test_messages_printer.py b/tests/unit/test_messages_printer.py
index 4d4e115..1def52d 100644
--- a/tests/unit/test_messages_printer.py
+++ b/tests/unit/test_messages_printer.py
@@ -634,7 +634,20 @@ def test_progress_bar_no_stream(recording_printer):
     assert recording_printer.prv_msg is None
 
 
-# -- tests for stopping the printer
+# -- tests for starting/stopping the printer
+
+
+def test_init_printer_ok(log_filepath):
+    """Printer is initiated as usual."""
+    printer = _Printer(log_filepath)
+    assert printer.spinner.is_alive()
+
+
+def test_init_printer_testmode(log_filepath, monkeypatch):
+    """Printer is initiated as usual."""
+    monkeypatch.setattr(messages, "TESTMODE", True)
+    printer = _Printer(log_filepath)
+    assert not printer.spinner.is_alive()
 
 
 def test_stop_streams_ok(capsys, log_filepath):
@@ -670,9 +683,17 @@ def test_stop_streams_unfinished_err(capsys, log_filepath):
     assert err == "\n"
 
 
-def test_stop_spinner(log_filepath):
+def test_stop_spinner_ok(log_filepath):
     """Stop the spinner."""
     printer = _Printer(log_filepath)
     assert printer.spinner.is_alive()
     printer.stop()
     assert not printer.spinner.is_alive()
+
+
+def test_stop_spinner_testmode(log_filepath, monkeypatch):
+    """Stop the spinner."""
+    monkeypatch.setattr(messages, "TESTMODE", True)
+    printer = _Printer(log_filepath)
+    printer.stop()
+    assert not printer.spinner.is_alive()