diff --git a/test/unit_tests/image_stitcher_test.py b/test/unit_tests/image_stitcher_test.py
index 267cd40..1ec60d4 100644
--- a/test/unit_tests/image_stitcher_test.py
+++ b/test/unit_tests/image_stitcher_test.py
@@ -40,8 +40,12 @@ def make_coord_getter(c):
     }[c]
 
 
-def make_pair_merger(direction):
-    return {"y": merge_pair_vertically, "x": merge_pair_horizontally}[direction]
+def make_pair_merger(axis):
+    return {"y": merge_pair_vertically, "x": merge_pair_horizontally}[axis]
+
+
+def make_group_merger(axis):
+    return {"y": merge_group_vertically, "x": merge_group_horizontally}[axis]
 
 
 def make_length_getter(dim):
@@ -165,11 +169,27 @@ def merge_group_vertically(group):
 
 class Stitcher:
     @staticmethod
-    def groupby(pairs, coord):
-        coord_getter = make_coord_getter(coord)
+    def groupby(pairs, coord_getter):
         pairs = sorted(pairs, key=coord_getter)
         return map(compose(list, second), groupby(pairs, coord_getter))
 
+    @staticmethod
+    def other_axis(axis):
+        return "y" if axis == "x" else "x"
+
+    def merge_along_axis(self, pairs, axis):
+
+        c1_getter = make_coord_getter(f"{self.other_axis(axis)}1")
+        c2_getter = make_coord_getter(f"{self.other_axis(axis)}2")
+        group_merger = make_group_merger(axis)
+
+        groups = self.groupby(pairs, c1_getter)
+        groups = chain.from_iterable(map(rpartial(self.groupby, c2_getter), groups))
+        groups = map(group_merger, groups)
+        pairs = chain.from_iterable(groups)
+
+        return pairs
+
     def stitch(self, pairs: Iterable[ImageMetadataPair]) -> List[ImageMetadataPair]:
 
         pairs = list(pairs)
@@ -177,18 +197,12 @@ class Stitcher:
 
         while True:
 
-            groups = self.groupby(pairs, "x1")
-            groups = chain.from_iterable(map(rpartial(self.groupby, "x2"), groups))
-            groups = map(merge_group_vertically, groups)
-            pairs = chain.from_iterable(groups)
-
-            groups = self.groupby(pairs, "y1")
-            groups = chain.from_iterable(map(rpartial(self.groupby, "y2"), groups))
-            groups = map(merge_group_horizontally, groups)
-            pairs = list(chain.from_iterable(groups))
+            pairs = self.merge_along_axis(pairs, "x")
+            pairs = list(self.merge_along_axis(pairs, "y"))
 
             if len(pairs) == n:
                 return pairs
+
             n = len(pairs)