Re-added problematic tests with notes

Author: JulVandenBroeck

tests/sparse/test_construct.pyi

@@ -269,17 +269,21 @@ assert_type(sparse.block_array([[coo_arr]], dtype=int), sparse.coo_array[np.int_
 assert_type(sparse.block_array([[csr_arr]], dtype=sctype), sparse.csr_array[ScalarType, tuple[int, int]])
 assert_type(sparse.block_array([[lil_arr]], dtype=np.complex64), sparse.coo_array[np.complex64, tuple[int, int]])
 assert_type(sparse.block_array([[csr_arr]], format="lil"), sparse.lil_array[ScalarType])
-assert_type(sparse.block_array([[coo_arr]], format="bsr", dtype="float"), sparse.bsr_array[np.float64])
-assert_type(sparse.block_array([[dia_arr]], format="dok", dtype=complex), sparse.dok_array[np.complex128])
+assert_type(sparse.block_array([[coo_arr, None]], format="bsr", dtype="float"), sparse.bsr_array[np.float64])
+assert_type(sparse.block_array([[dia_arr], [None]], format="dok", dtype=complex), sparse.dok_array[np.complex128])
+# NOTE: mypy reports false positive errors here, because of join vs. union approach
+assert_type(sparse.block_array([[csr_arr, None], [None, dok_arr]], format="dia"), sparse.dia_array[ScalarType])  # type: ignore[assert-type]
+
 # bmat (legacy, `block_array` is p`referred)
 assert_type(sparse.bmat([[bsr_mat]]), sparse.coo_matrix[ScalarType])
-assert_type(sparse.bmat([[csr_mat]]), sparse.csr_matrix[ScalarType])
 assert_type(sparse.bmat([[dia_mat]], dtype=np.int_), sparse.coo_matrix[np.int_])
-assert_type(sparse.bmat([[dok_mat]], dtype=np.complex64), sparse.coo_matrix[np.complex64])
 assert_type(sparse.bmat([[bsr_arr]]), sparse.coo_array[ScalarType, tuple[int, int]])
-assert_type(sparse.bmat([[csr_arr]]), sparse.csr_array[ScalarType, tuple[int, int]])
 assert_type(sparse.bmat([[dia_arr]], dtype=np.int_), sparse.coo_array[np.int_, tuple[int, int]])
-assert_type(sparse.bmat([[dok_arr]], dtype=np.complex64), sparse.coo_array[np.complex64, tuple[int, int]])
+# NOTE: mypy reports false positive errors here, because of join vs. union approach
+assert_type(sparse.bmat([[csr_mat], [None]]), sparse.csr_matrix[ScalarType])  # type: ignore[assert-type,arg-type]
+assert_type(sparse.bmat([[dok_mat], [None]], dtype=np.complex64), sparse.coo_matrix[np.complex64])  # type: ignore[assert-type,arg-type]
+assert_type(sparse.bmat([[csr_arr], [None]]), sparse.csr_array[ScalarType, tuple[int, int]])  # type: ignore[assert-type,arg-type]
+assert_type(sparse.bmat([[dok_arr], [None]], dtype=np.complex64), sparse.coo_array[np.complex64, tuple[int, int]])  # type: ignore[assert-type,arg-type]
 
 # block_diag
 assert_type(sparse.block_diag([any_arr, any_arr]), sparse.coo_array[ScalarType, tuple[int, int]])