add tests for negative use cases to improve covergae

tests/test_arraycreation.py

@@ -129,6 +129,15 @@ def test_diag_diagflat(v, k):
     assert_array_equal(expected, result)
 
 
+def test_diag_diagflat_raise_error():
+    ia = dpnp.array([0, 1, 2, 3, 4])
+    with pytest.raises(TypeError):
+        dpnp.diag(ia, k=2.0)
+
+    with pytest.raises(TypeError):
+        dpnp.diagflat(ia, k=2.0)
+
+
 @pytest.mark.parametrize(
     "seq",
     [
@@ -488,6 +497,16 @@ def test_vander(array, dtype, n, increase):
     assert_allclose(vander_func(numpy, a_np), vander_func(dpnp, a_dpnp))
 
 
+def test_vander_raise_error():
+    a = dpnp.array([1, 2, 3, 4])
+    with pytest.raises(TypeError):
+        dpnp.vander(a, N=1.0)
+
+    a = dpnp.array([[1, 2], [3, 4]])
+    with pytest.raises(ValueError):
+        dpnp.vander(a)
+
+
 @pytest.mark.parametrize(
     "sequence",
     [[1, 2, 3, 4], (1, 2, 3, 4)],