diff --git a/tests/test_NXclassWriters.py b/tests/test_NXclassWriters.py
index 404d5a6a..e51a9291 100644
--- a/tests/test_NXclassWriters.py
+++ b/tests/test_NXclassWriters.py
@@ -1,13 +1,48 @@
 import tempfile
 from datetime import datetime
+from unittest.mock import MagicMock
 
 import h5py
 import pytest
+import numpy as np
+from pathlib import Path
+from numpy.testing import assert_array_equal
 
-from nexgen.nxs_write.NXclassWriters import write_NXdatetime, write_NXdetector_module
+from nexgen.nxs_write.NXclassWriters import (
+    write_NXdatetime,
+    write_NXdetector_module,
+    write_NXdata,
+    write_NXsample,
+)
 
 test_module = {"fast_axis": [1, 0, 0], "slow_axis": [0, 1, 0]}
 
+test_goniometer_axes = {
+    "axes": ["omega", "sam_z", "sam_y"],
+    "depends": [".", "omega", "sam_z"],
+    "vectors": [
+        -1,
+        0,
+        0,
+        0,
+        -1,
+        0,
+        -1,
+        0,
+        0,
+    ],
+    "types": [
+        "rotation",
+        "translation",
+        "translation",
+    ],
+    "units": ["deg", "mm", "mm"],
+    "offsets": [0, 0, 0, 0, 0, 0, 0, 0, 0],
+    "starts": [0, 0, 0],
+    "ends": [90, 0, 0],
+    "increments": [1, 0, 0],
+}
+
 
 @pytest.fixture
 def dummy_nexus_file():
@@ -16,6 +51,104 @@ def dummy_nexus_file():
     yield test_nexus_file
 
 
+def test_given_no_data_files_when_write_NXdata_then_assert_error():
+    mock_hdf5_file = MagicMock()
+    with pytest.raises(OSError):
+        write_NXdata(mock_hdf5_file, [], {}, "", "", [])
+
+
+def test_given_no_data_type_specified_when_write_NXdata_then_exception_raised(
+    dummy_nexus_file,
+):
+    osc_scan = {"omega": np.arange(0, 90, 1)}
+    with pytest.raises(ValueError):
+        write_NXdata(
+            dummy_nexus_file,
+            [Path("tmp")],
+            test_goniometer_axes,
+            ("", 0),
+            "",
+            osc_scan,
+        )
+
+
+def test_given_one_data_file_when_write_NXdata_then_data_in_file(
+    dummy_nexus_file,
+):
+    osc_scan = {"omega": np.arange(0, 90, 1)}
+    write_NXdata(
+        dummy_nexus_file,
+        [Path("tmp")],
+        test_goniometer_axes,
+        ("images", 0),
+        "",
+        osc_scan,
+    )
+    assert dummy_nexus_file["/entry/data"].attrs["NX_class"] == b"NXdata"
+    assert "data_000001" in dummy_nexus_file["/entry/data"]
+
+
+def test_given_scan_axis_when_write_NXdata_then_axis_in_data_entry_with_correct_data_and_attributes(
+    dummy_nexus_file,
+):
+    test_axis = "omega"
+    test_scan_range = np.arange(0, 90, 1)
+    axis_entry = f"/entry/data/{test_axis}"
+    osc_scan = {test_axis: test_scan_range}
+
+    write_NXdata(
+        dummy_nexus_file,
+        [Path("tmp")],
+        test_goniometer_axes,
+        ("images", 0),
+        "",
+        osc_scan,
+    )
+
+    assert test_axis in dummy_nexus_file["/entry/data"]
+    assert_array_equal(test_scan_range, dummy_nexus_file[axis_entry][:])
+    assert dummy_nexus_file[axis_entry].attrs["depends_on"] == b"."
+    assert dummy_nexus_file[axis_entry].attrs["transformation_type"] == b"rotation"
+    assert dummy_nexus_file[axis_entry].attrs["units"] == b"deg"
+    assert_array_equal(dummy_nexus_file[axis_entry].attrs["vector"][:], [-1.0, 0.0, 0])
+
+
+def test_given_scan_axis_when_write_NXsample_then_scan_axis_data_copied_from_data_group_as_well_as_increment_set_and_end(
+    dummy_nexus_file,
+):
+    test_axis = "omega"
+    test_scan_range = [0, 1, 2]
+    axis_entry = f"/entry/sample/sample_{test_axis}/{test_axis}"
+    osc_scan = {test_axis: test_scan_range}
+
+    # Doing this to write the scan axis data into the data group
+    write_NXdata(
+        dummy_nexus_file,
+        [Path("tmp")],
+        test_goniometer_axes,
+        ("images", 0),
+        "",
+        osc_scan,
+    )
+
+    write_NXsample(
+        dummy_nexus_file,
+        test_goniometer_axes,
+        "",
+        ("images", 0),
+        osc_scan,
+    )
+
+    assert f"sample_{test_axis}" in dummy_nexus_file["/entry/sample"]
+    assert_array_equal(test_scan_range, dummy_nexus_file[axis_entry][:])
+    assert dummy_nexus_file[axis_entry].attrs["depends_on"] == b"."
+    assert dummy_nexus_file[axis_entry].attrs["transformation_type"] == b"rotation"
+    assert dummy_nexus_file[axis_entry].attrs["units"] == b"deg"
+    assert_array_equal(dummy_nexus_file[axis_entry].attrs["vector"][:], [-1, 0, 0])
+    assert_array_equal(dummy_nexus_file[axis_entry + "_increment_set"][:], [1] * 3)
+    assert dummy_nexus_file[axis_entry + "_end"][1] == 2
+
+
 def test_given_module_offset_of_1_when_write_NXdetector_module_then_fast_and_slow_axis_depends_on_module_offset(
     dummy_nexus_file,
 ):