Added functions to test linkage functions.

Currently they take up a lot of processing. Pulling them out, gives us
an easier way to test them and subsequently try to improve them.

Author: exhuma

cluster/test/test_linkage.py

@@ -0,0 +1,31 @@
+import unittest
+
+from cluster.linkage import single, complete, uclus, average
+
+
+class LinkageMethods(unittest.TestCase):
+
+    def setUp(self):
+        self.set_a = [1, 2, 3, 4]
+        self.set_b = [10, 11, 12, 13, 14, 15, 100]
+        self.dist = lambda x, y: abs(x-y)  # NOQA
+
+    def test_single_distance(self):
+        result = single(self.set_a, self.set_b, self.dist)
+        expected = 6
+        self.assertEqual(result, expected)
+
+    def test_complete_distance(self):
+        result = complete(self.set_a, self.set_b, self.dist)
+        expected = 99
+        self.assertEqual(result, expected)
+
+    def test_uclus_distance(self):
+        result = uclus(self.set_a, self.set_b, self.dist)
+        expected = 10.5
+        self.assertEqual(result, expected)
+
+    def test_average_distance(self):
+        result = average(self.set_a, self.set_b, self.dist)
+        expected = 22.5
+        self.assertEqual(result, expected)