Add unittests for empty sparse matrix loading (#58)

* Fixed issue with loading all-zero sparse matrices, as the data and ir pointers are not stored in the .mat file.

* add unittest

---------

Co-authored-by: S. Breedveld <[email protected]>

tests/create_mat.m

@@ -41,7 +41,9 @@
 
 clear all
 
-%% second created file
+%% second created file for https://github.com/skjerns/mat7.3/pull/57
 
-data.x1 = {'test', 'asd'};
-data.x2 = {{1,2,3}, {1,2,3}};
+A = sparse([0 0 0; 0 0 0]);
+save('testfile13.mat','-v7.3')
+clear all
+%% 

tests/test_mat73.py

@@ -34,7 +34,7 @@ class Testing(unittest.TestCase):
 
     def setUp(self):
         """make links to test files and make sure they are present"""
-        for i in range(1, 13):
+        for i in range(1, 14):
             file = 'testfile{}.mat'.format(i)
             if not os.path.exists(file):
                 file = os.path.join('./tests', file)
@@ -425,6 +425,19 @@ def test_file12_sparse_matrix_fix(self):
         assert isinstance(struct_sparse[0]['stim_pattern'], sparse_type)
         assert isinstance(struct_sparse[0]['stimulation'], str)
 
+    def test_file13_empty_sparse_matrix(self):
+        """some sparse matrices could not be loaded. check if it now works"""
+        # check regular loading works
+        import scipy
+        data = mat73.loadmat(self.testfile13)
+        struct_sparse = data['A']
+        sparse_type = scipy.sparse.csc_matrix
+        assert isinstance(struct_sparse, sparse_type)
+        assert struct_sparse.getnnz()==0
+        assert struct_sparse.sum()==0
+        assert (struct_sparse.toarray()==np.zeros([2,3])).all()
+        assert struct_sparse.shape==(2, 3)
+
 
 if __name__ == '__main__':