diff --git a/autoconf/test_mode.py b/autoconf/test_mode.py
index b22d8e7..22b14ba 100644
--- a/autoconf/test_mode.py
+++ b/autoconf/test_mode.py
@@ -1,4 +1,5 @@
 import os
+from pathlib import Path
 
 
 def test_mode_level():
@@ -61,3 +62,32 @@ def skip_latents():
     ``compute_latent_samples`` pass.
     """
     return is_test_mode() or os.environ.get("PYAUTO_SKIP_LATENTS", "0") == "1"
+
+
+def with_test_mode_segment(base: Path) -> Path:
+    """
+    Return ``base`` with a ``test_mode`` segment appended when
+    ``PYAUTO_TEST_MODE`` is active, else return ``base`` unchanged.
+
+    Workspace scripts that compose their own output paths (e.g. the
+    ``guides/results/aggregator/`` tutorials in ``autolens_workspace`` and
+    ``autogalaxy_workspace``) must agree with PyAutoFit's internal
+    ``_test_mode_segment`` (``autofit/non_linear/paths/abstract.py``), which
+    inserts ``output/test_mode/...`` whenever ``PYAUTO_TEST_MODE`` is set.
+    This helper exposes the same namespacing rule so workspace path
+    composition stays consistent without duplicating the env-var check.
+
+    The name avoids a leading ``test_`` so pytest does not try to
+    collect callsites in test modules as test functions.
+
+    Examples
+    --------
+    >>> # PYAUTO_TEST_MODE unset
+    >>> with_test_mode_segment(Path("output")) / "results_folder"
+    PosixPath('output/results_folder')
+
+    >>> # PYAUTO_TEST_MODE=2
+    >>> with_test_mode_segment(Path("output")) / "results_folder"
+    PosixPath('output/test_mode/results_folder')
+    """
+    return base / "test_mode" if is_test_mode() else base
diff --git a/test_autoconf/test_test_mode.py b/test_autoconf/test_test_mode.py
new file mode 100644
index 0000000..5b27c8b
--- /dev/null
+++ b/test_autoconf/test_test_mode.py
@@ -0,0 +1,56 @@
+"""Tests for autoconf.test_mode helpers — focused on
+``with_test_mode_segment`` since the other helpers (``is_test_mode``,
+``skip_fit_output``, etc.) are exercised by PyAutoFit/PyAutoArray
+integration tests downstream."""
+
+import os
+from pathlib import Path
+
+import pytest
+
+from autoconf.test_mode import (
+    is_test_mode,
+    test_mode_level,
+    with_test_mode_segment,
+)
+
+
+@pytest.fixture(autouse=True)
+def _restore_test_mode_env():
+    """Save/restore PYAUTO_TEST_MODE around each test so a failure
+    can't leak state to its neighbours."""
+
+    saved = os.environ.get("PYAUTO_TEST_MODE")
+    yield
+    if saved is None:
+        os.environ.pop("PYAUTO_TEST_MODE", None)
+    else:
+        os.environ["PYAUTO_TEST_MODE"] = saved
+
+
+def test_with_test_mode_segment__env_unset_returns_base_unchanged():
+    os.environ.pop("PYAUTO_TEST_MODE", None)
+    assert with_test_mode_segment(Path("output")) == Path("output")
+
+
+def test_with_test_mode_segment__env_zero_returns_base_unchanged():
+    """``PYAUTO_TEST_MODE=0`` is the documented off state, so the
+    helper must treat it the same as unset (no test_mode segment)."""
+    os.environ["PYAUTO_TEST_MODE"] = "0"
+    assert is_test_mode() is False
+    assert with_test_mode_segment(Path("output")) == Path("output")
+
+
+@pytest.mark.parametrize("level", ["1", "2", "3"])
+def test_with_test_mode_segment__env_set_inserts_segment(level):
+    os.environ["PYAUTO_TEST_MODE"] = level
+    assert with_test_mode_segment(Path("output")) == Path("output") / "test_mode"
+
+
+def test_with_test_mode_segment__chains_with_pathlib_concat():
+    """The helper's return value must compose with further ``/`` ops so
+    workspace scripts can write ``with_test_mode_segment(base) / 'name'``
+    in a single line."""
+    os.environ["PYAUTO_TEST_MODE"] = "2"
+    composed = with_test_mode_segment(Path("output")) / "results_folder"
+    assert composed == Path("output") / "test_mode" / "results_folder"