diff --git a/packages/essnmx/src/ess/nmx/data/__init__.py b/packages/essnmx/src/ess/nmx/data/__init__.py
index ece282a9c..4363adac2 100644
--- a/packages/essnmx/src/ess/nmx/data/__init__.py
+++ b/packages/essnmx/src/ess/nmx/data/__init__.py
@@ -29,6 +29,9 @@
         "small_nmx_nexus.hdf.zip": Entry(
             alg="md5", chk="96877cddc9f6392c96890069657710ca", extractor="unzip"
         ),
+        "essnmx-reduced-26.4.1.hdf.zip": Entry(
+            alg="md5", chk="f7877cce3967dec0aa51461c1100824d", extractor="unzip"
+        ),
     },
 )
 
@@ -75,3 +78,15 @@ def get_small_nmx_nexus() -> pathlib.Path:
     """Return the path to a small NMX NeXus file."""
 
     return get_path("small_nmx_nexus.hdf.zip")
+
+
+def get_small_nmx_reduced() -> pathlib.Path:
+    """Return the path to a reduced NXlauetof file.
+
+    It is reduced from the small nmx nexus file
+    using specific version of essnmx.
+    It is frozen as reference file to check if the output
+    of essnmx-reduce changed.
+    """
+
+    return get_path("essnmx-reduced-26.4.1.hdf.zip")
diff --git a/packages/essnmx/tests/executable_output_test.py b/packages/essnmx/tests/executable_output_test.py
new file mode 100644
index 000000000..0bfc85854
--- /dev/null
+++ b/packages/essnmx/tests/executable_output_test.py
@@ -0,0 +1,109 @@
+# SPDX-License-Identifier: BSD-3-Clause
+# Copyright (c) 2026 Scipp contributors (https://github.com/scipp)
+"""Compare the workflow output to be consistent with the reference output file.
+
+This test detects any changes in the output file.
+If anything must change, consult the IDS member
+and update the frozen file in the `ess.nmx.data` registry.
+"""
+
+import pathlib
+
+# The bitshuffle plugin needs to be imported at least once in the session
+# so that h5py can use the plugin.
+import bitshuffle.h5  # noqa: F401
+import h5py
+import numpy as np
+import pytest
+
+from ess.nmx.configurations import (
+    InputConfig,
+    OutputConfig,
+    ReductionConfig,
+    WorkflowConfig,
+)
+from ess.nmx.data import get_small_nmx_nexus, get_small_nmx_reduced
+from ess.nmx.executables import reduction
+from ess.nmx.types import Compression
+
+
+def assert_h5_attrs_equal(
+    attrs_left: h5py.AttributeManager,
+    attrs_right: h5py.AttributeManager,
+    cur_path: pathlib.Path,
+) -> None:
+
+    assert attrs_left.keys() == attrs_right.keys()
+    for attr_key, attr in attrs_left.items():
+        if not isinstance(attr, str) and hasattr(attr, '__len__'):
+            assert all(attr == attrs_right[attr_key]), cur_path
+        else:
+            assert attr == attrs_right[attr_key], cur_path
+
+
+def assert_h5obj_equal(
+    obj_left: h5py.Group | h5py.Dataset,
+    obj_right: h5py.Group | h5py.Dataset,
+    _cur_path: pathlib.Path = pathlib.Path('/'),
+    excluded_paths: tuple[pathlib.Path, ...] = (),
+) -> None:
+    assert type(obj_left) is type(obj_right)
+    assert_h5_attrs_equal(obj_left.attrs, obj_right.attrs, _cur_path)
+    if isinstance(obj_left, h5py.Group) and isinstance(obj_right, h5py.Group):
+        for key in obj_left.keys():
+            cur_sub_path = _cur_path / key
+            if cur_sub_path in excluded_paths:
+                continue
+            else:
+                assert key in obj_right
+                assert_h5obj_equal(
+                    obj_left[key],
+                    obj_right[key],
+                    _cur_path=cur_sub_path,
+                    excluded_paths=excluded_paths,
+                )
+    else:
+        values_left = obj_left[()]
+        values_right = obj_right[()]
+        assert type(values_left) is type(values_right)
+        if not isinstance(values_left, np.ndarray) or not isinstance(
+            values_right, np.ndarray
+        ):
+            assert values_left == values_right, _cur_path
+        else:
+            assert values_left.shape == values_right.shape, _cur_path
+            # We use np.allclose instead of np.all(left==right)
+            # since some reduction operations might give a small difference every time.
+            # Tolerance of 1e-13 was decided since assertion starts failing at 1e-15
+            assert np.allclose(values_left, values_right, rtol=1e-13, atol=1e-13), (
+                _cur_path
+            )
+
+
+def test_compare_output_file_with_frozen(tmp_path: pathlib.Path):
+    """Test that the executable runs and returns the expected output."""
+
+    # Make a new output file from current implementation.
+    input_file = get_small_nmx_nexus()
+    output_file = tmp_path / "scipp_output_current.h5"
+    assert not output_file.exists()
+    config = ReductionConfig(
+        inputs=InputConfig(input_file=[input_file.as_posix()]),
+        workflow=WorkflowConfig(),
+        output=OutputConfig(
+            output_file=output_file.as_posix(),
+            compression=Compression.NONE,
+            skip_file_output=False,
+        ),
+    )
+    with pytest.warns(RuntimeWarning, match="No crystal rotation*"):
+        _ = reduction(config=config)
+
+    entry_path = pathlib.Path('/entry')
+    excluded_paths = (
+        entry_path / 'reducer/program',  # version should be different
+    )
+    ref_file_path = get_small_nmx_reduced()
+    with h5py.File(output_file) as cur_file:
+        with h5py.File(ref_file_path) as reference_file:
+            assert_h5obj_equal(reference_file, cur_file, excluded_paths=excluded_paths)