--- a
+++ b/tests/test_blockzip.py
@@ -0,0 +1,54 @@
+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+import unittest
+from singlecellmultiomics.utils import BlockZip
+
+import os
+"""
+These tests check if the BlockZip module is working correctly
+"""
+
+class Test_BlockZip(unittest.TestCase):
+
+    def test_read_write(self):
+        zip_path = './data/test.bgzf'
+        with BlockZip(zip_path,'w') as f:
+            f.write('chr1',100,False,'yes')
+            f.write('chr1',101,False,'yes')
+            f.write('chr2',2101,True,'yes')
+            f.write('chrX',0,False,'X')
+
+        with BlockZip(zip_path,'r') as f:
+            self.assertEqual( f[ ('chr1',100,False) ], 'yes' )
+            self.assertEqual( f[ ('chr1',0,False) ], None)
+            self.assertEqual( f[ ('chrX',0,False) ], 'X' )
+            self.assertEqual( f[ ('chr2',2101,True) ], 'yes' )
+            self.assertEqual( f[ ('chr1',0,True) ], None)
+
+
+        # Test verification:
+        with BlockZip(zip_path,'r') as f:
+            f.verify()
+
+        with BlockZip(zip_path,'w') as f:
+            f.write('chr1',101,False,'yes')
+            f.write('chr1',100,False,'yes')
+            f.write('chr2',2101,True,'yes')
+            f.write('chrX',0,False,'X')
+
+        with BlockZip(zip_path,'r') as bz:
+            self.assertRaises(ValueError, bz.verify)
+
+
+        # Test for missing index:
+        os.remove(zip_path+'.idx')
+        self.assertRaises(ValueError, BlockZip, './non_existing.bgzf','r')
+
+        os.remove(zip_path)
+        self.assertRaises(ValueError, BlockZip, './non_existing.bgzf','r')
+
+
+
+
+if __name__ == '__main__':
+    unittest.main()