added add test

test/test_add.py

+from nose.tools import assert_equal
+
+import torch
 from torch_scatter._ext import scatter
 
 
 def test_scatter_add():
-    pass
+    input = [[2, 0, 1, 4, 3], [0, 2, 1, 3, 4]]
+    index = [[4, 5, 4, 2, 3], [0, 0, 2, 2, 1]]
+    input = torch.FloatTensor(input)
+    index = torch.LongTensor(index)
+    output = input.new(2, 6).fill_(0)
+    expected_output = [[0, 0, 4, 3, 3, 0], [2, 4, 4, 0, 0, 0]]
+
+    scatter.scatter_add_Float(output, index, input, 1)
+    assert_equal(output.tolist(), expected_output)
+
+    n = 10000
+    input = torch.rand(torch.Size([n]))
+    index = (torch.rand(torch.Size([n])) * n).long()
+    output = input.new(n).fill_(0)
+    expected_output = input.new(n).fill_(0)
+    scatter.scatter_add_Float(output, index, input, 0)
+    expected_output.scatter_add_(0, index, input)
+
+    assert_equal(output.tolist(), expected_output.tolist())