diff --git a/tests/utils/numpy/test_hstack.py b/tests/utils/numpy/test_hstack.py
new file mode 100644
index 00000000..d405f20c
--- /dev/null
+++ b/tests/utils/numpy/test_hstack.py
@@ -0,0 +1,46 @@
+import numpy as np
+import pyunitwizard as puw
+import pytest
+
+
+def configure_libraries():
+    puw.configure.reset()
+    puw.configure.load_library(["pint", "openmm.unit"])
+
+
+def test_hstack_numpy_array_with_unit_conversion():
+    configure_libraries()
+
+    sequence = [
+        [puw.quantity(1, "nanometer"), puw.quantity(2, "nanometer")],
+        [puw.quantity(10, "angstrom"), puw.quantity(20, "angstrom")],
+    ]
+
+    quantity = puw.utils.numpy.hstack(sequence, to_unit="nanometer", value_type="numpy.ndarray")
+    value = puw.get_value(quantity)
+
+    np.testing.assert_allclose(value, [1.0, 2.0, 1.0, 2.0])
+    assert str(puw.get_unit(quantity)) == "nanometer"
+
+
+def test_hstack_list_value_type_matches_expected_values():
+    configure_libraries()
+
+    sequence = [
+        [puw.quantity(1, "meter"), puw.quantity(2, "meter")],
+        [puw.quantity(3, "meter"), puw.quantity(4, "meter")],
+    ]
+
+    quantity = puw.utils.numpy.hstack(sequence, value_type="list")
+    value = puw.get_value(quantity)
+
+    np.testing.assert_array_equal(value, [1, 2, 3, 4])
+
+
+def test_hstack_invalid_value_type_raises_value_error():
+    configure_libraries()
+
+    sequence = [[puw.quantity(1, "meter")]]
+
+    with pytest.raises(ValueError):
+        puw.utils.numpy.hstack(sequence, value_type="dictionary")
diff --git a/tests/utils/numpy/test_vstack.py b/tests/utils/numpy/test_vstack.py
new file mode 100644
index 00000000..211d3e65
--- /dev/null
+++ b/tests/utils/numpy/test_vstack.py
@@ -0,0 +1,46 @@
+import numpy as np
+import pyunitwizard as puw
+import pytest
+
+
+def configure_libraries():
+    puw.configure.reset()
+    puw.configure.load_library(["pint", "openmm.unit"])
+
+
+def test_vstack_numpy_array_shape():
+    configure_libraries()
+
+    sequence = [
+        [puw.quantity([1, 2], "nanometer")],
+        [puw.quantity([10, 20], "angstrom")],
+    ]
+
+    quantity = puw.utils.numpy.vstack(sequence, to_unit="nanometer", value_type="numpy.ndarray")
+    value = puw.get_value(quantity)
+
+    assert value.shape == (2, 2)
+    np.testing.assert_allclose(value, [[1.0, 2.0], [1.0, 2.0]])
+
+
+def test_vstack_tuple_value_type_matches_expected_values():
+    configure_libraries()
+
+    sequence = [
+        [puw.quantity([1, 2], "meter")],
+        [puw.quantity([3, 4], "meter")],
+    ]
+
+    quantity = puw.utils.numpy.vstack(sequence, value_type="tuple")
+    value = puw.get_value(quantity)
+
+    np.testing.assert_array_equal(value, [[1, 2], [3, 4]])
+
+
+def test_vstack_invalid_value_type():
+    configure_libraries()
+
+    sequence = [[puw.quantity(1, "meter")]]
+
+    with pytest.raises(ValueError):
+        puw.utils.numpy.vstack(sequence, value_type="set")