Add NearestNeighbour unit test

tests/test_kdtree.py

@@ -1,8 +1,9 @@
 import numpy as np
 import pytest
-from signalflow import KDTree
+from signalflow import KDTree, NearestNeighbour, Buffer
+from . import graph
 
-def test_kdtree():
+def test_kdtree(graph):
     corpus = np.random.uniform(0, 10, [1024, 2])
     tree = KDTree(corpus)
     target = np.array([1, 5])
@@ -23,6 +24,13 @@ def test_kdtree():
     # (subject to rounding error)
     assert nearest.distance == pytest.approx(np.linalg.norm(corpus[nearest.index] - target), abs=1e-6)
 
+    # confirm that the NearestNeighbour node returns the same value,
+    # constructing a buffer storing the corpus coordinates
+    buffer = Buffer(corpus.T)
+    nearest_neighbour = NearestNeighbour(buffer, target=target)
+    graph.render_subgraph(nearest_neighbour)
+    assert nearest_neighbour.output_buffer[0][0] == nearest.index
+
 def test_kdtree_validation():
     corpus = np.random.uniform(0, 10, [1024, 2])
     tree = KDTree(corpus)