--- a
+++ b/tests/tissues/test_tissue.py
@@ -0,0 +1,31 @@
+import unittest
+
+import numpy as np
+
+from dosma.tissues.tissue import largest_cc
+
+
+class TestLargestCC(unittest.TestCase):
+    def test_largest_cc(self):
+        # smallest cc
+        a = np.zeros((100, 100)).astype(np.uint8)
+        a[:10, :10] = 1
+
+        # medium cc
+        b = np.zeros((100, 100)).astype(np.uint8)
+        b[85:, 85:] = 1
+
+        # largest cc
+        c = np.zeros((100, 100)).astype(np.uint8)
+        c[25:75, 25:75] = 1
+
+        mask = a | b | c
+
+        assert np.all(largest_cc(mask) == c)  # only largest cc returned
+        assert np.all(largest_cc(mask, num=2) == (b | c))  # largest 2 cc
+        assert np.all(largest_cc(mask, num=3) == (a | b | c))  # largest 3 cc
+        assert np.all(largest_cc(mask, num=4) == (a | b | c))  # only 3 cc, return all
+
+
+if __name__ == "__main__":
+    unittest.main()