Added unit tests for the lower function (#20)

* Added unit tests for the lower function

* Fixed import formatting, black and flake8 automatic checks

---------

Co-authored-by: Chaluvadi <saketh.chaluvadi@intel.com>

Author: sakchal

tests/test_lower.py

@@ -0,0 +1,45 @@
+import pytest
+
+import arrayfire_wrapper.dtypes as dtypes
+import arrayfire_wrapper.lib as wrapper
+
+
+@pytest.mark.parametrize(
+    "shape",
+    [
+        (3, 3),
+        (3, 3, 3),
+        (3, 3, 3, 3),
+    ],
+)
+def test_diag_is_unit(shape: tuple) -> None:
+    """Test if when is_unit_diag in lower returns an array with a unit diagonal"""
+    dtype = dtypes.s64
+    constant_array = wrapper.constant(3, shape, dtype)
+
+    lower_array = wrapper.lower(constant_array, True)
+    diagonal = wrapper.diag_extract(lower_array, 0)
+    diagonal_value = wrapper.get_scalar(diagonal, dtype)
+
+    assert diagonal_value == 1
+
+
+@pytest.mark.parametrize(
+    "shape",
+    [
+        (3, 3),
+        (3, 3, 3),
+        (3, 3, 3, 3),
+    ],
+)
+def test_is_original(shape: tuple) -> None:
+    """Test if is_original keeps the diagonal the same as the original array"""
+    dtype = dtypes.s64
+    constant_array = wrapper.constant(3, shape, dtype)
+    original_value = wrapper.get_scalar(constant_array, dtype)
+
+    lower_array = wrapper.lower(constant_array, False)
+    diagonal = wrapper.diag_extract(lower_array, 0)
+    diagonal_value = wrapper.get_scalar(diagonal, dtype)
+
+    assert original_value == diagonal_value