Check that distance from A to B is same as from B to A

Issue:
https://github.com/genenetwork/gn-gemtext-threads/blob/main/topics/gn1-migration-to-gn2/clustering.gmi

* gn3/computations/slink.py: check that the distance from child A to B is the
  same as distance from child B to A. If not, throw an exception.

* tests/unit/computations/test_slink.py:
  * Change the name of the test to more closely correspond to the business
    logic being tested.
  * Update the data in a separate test such that it does not error out due to
    failing to fulfill the expectations of separate requirement.

- pass tests
- Rename test
- Fix errors: distances same both directions

2 files changed, 19 insertions, 7 deletions

diff --git a/gn3/computations/slink.py b/gn3/computations/slink.py
index f3a6951..928330d 100644
--- a/gn3/computations/slink.py
+++ b/gn3/computations/slink.py
@@ -35,6 +35,17 @@ def raise_valueerror_if_child_list_distance_from_itself_is_not_zero(lists):
     if not all(map(distance_is_zero, children_distances)):
         raise ValueError("Distance of each child list/tuple from itself should be zero!")
 
+def raise_mirrorerror_of_distances_one_way_are_not_same_other_way(lists):
+    """Check that the distance from A to B, is the same as the distance from B to A.
+If the two distances are different, throw an exception."""
+    for i in range(len(lists)):
+        for j in range(len(lists)):
+            if lists[i][j] != lists[j][i]:
+                raise MirrorError(
+                    ("Distance from one child({}) to the other ({}) "
+                     "should be the same in both directions.").format(
+                         lists[i][j], lists[j][i]))
+
 def nearest(lists, i, j):
     """Computes some form of distance.
 This is 'copied' over from genenetwork1, from https://github.com/genenetwork/genenetwork1/blob/master/web/webqtl/heatmap/slink.py#L42-L64.
@@ -46,5 +57,6 @@ This description should be updated once the form/type of 'distance' identified."
     raise_valueerror_if_lists_empty(lists)
     raise_lengtherror_if_child_lists_are_not_same_as_parent(lists)
     raise_valueerror_if_child_list_distance_from_itself_is_not_zero(lists)
+    raise_mirrorerror_of_distances_one_way_are_not_same_other_way(lists)
     #### END: Guard Functions ####
     return None
diff --git a/tests/unit/computations/test_slink.py b/tests/unit/computations/test_slink.py
index 1fb7bbb..207debf 100644
--- a/tests/unit/computations/test_slink.py
+++ b/tests/unit/computations/test_slink.py
@@ -44,7 +44,7 @@ class TestSlink(TestCase):
                 with self.assertRaises(ValueError):
                     nearest(lst, 1, 1)
 
-    def test_nearest_expects_exception_if_value_at_index_j_in_list_i_does_not_equals_value_at_index_i_in_list_j(self):
+    def test_nearest_expects_exception_if_distance_from_child_a_to_child_b_is_not_distance_from_child_b_to_child_a(self):
         for lst in [[[0,1],[2,0]],
                     [[0,1,2],[1,0,3],[9,7,0]],
                     [[0,1,2,3],[7,0,2,3],[2,3,0,1],[8,9,5,0]]]:
@@ -56,12 +56,12 @@ class TestSlink(TestCase):
         # Based on:
         # https://github.com/genenetwork/genenetwork1/blob/master/web/webqtl/heatmap/slink.py#L87-L89
         for lst in [[[0,1,2,3],[1,0,3,4],[2,3,0,5],[3,4,5,0]],
-                    [[0,1,2,3],[-1,0,3,4],[2,3,0,5],[3,4,5,0]],
-                    [[0,1,2,3],[1,0,3,4],[-2,3,0,5],[3,4,5,0]],
-                    [[0,1,2,3],[1,0,3,4],[2,-3,0,5],[3,4,5,0]],
-                    [[0,1,2,3],[1,0,3,4],[2,3,0,5],[-3,4,5,0]],
-                    [[0,1,2,3],[1,0,3,4],[2,3,0,5],[3,-4,5,0]],
-                    [[0,1,2,3],[1,0,3,4],[2,3,0,5],[3,4,-5,0]]]:
+                    [[0,-1,2,3],[-1,0,3,4],[2,3,0,5],[3,4,5,0]],
+                    [[0,1,-2,3],[1,0,3,4],[-2,3,0,5],[3,4,5,0]],
+                    [[0,1,2,3],[1,0,-3,4],[2,-3,0,5],[3,4,5,0]],
+                    [[0,1,2,-3],[1,0,3,4],[2,3,0,5],[-3,4,5,0]],
+                    [[0,1,2,3],[1,0,3,-4],[2,3,0,5],[3,-4,5,0]],
+                    [[0,1,2,3],[1,0,3,4],[2,3,0,-5],[3,4,-5,0]]]:
             with self.subTest(lst=lst):
                 with self.assertRaises(ValueError, msg="Got an unexpected negative value!"):
                     nearest(lst, 1, 1)