Add ply2txt unit test

tests/danesfield/data/octahedron.ply

@@ -0,0 +1,16 @@
+ply
+format ascii 1.0
+element vertex 6
+property float64 x
+property float64 y
+property float64 z
+property uint8 red
+property uint8 green
+property uint8 blue
+end_header
+-1.0 1.0 0.0 255 0 0
+-1.0 -1.0 0.0 0 255 0
+1.0 -1.0 0.0 0 0 255
+1.0 1.0 0.0 255 0 255
+0.0 0.0 0.7 255 255 255
+0.0 0.0 -0.7 0 0 0

tests/danesfield/tools/test_ply2txt.py

@@ -0,0 +1,29 @@
+###############################################################################
+# Copyright Kitware Inc. and Contributors
+# Distributed under the Apache License, 2.0 (apache.org/licenses/LICENSE-2.0)
+# See accompanying Copyright.txt and LICENSE files for details
+###############################################################################
+
+from tools.ply2txt import convert
+from os.path import dirname, join
+from os import remove
+
+data_dir = join(dirname(dirname(__file__)), 'data')
+
+
+def test_ply2txt():
+    ply_source = join(data_dir, 'octahedron.ply')
+    txt_target = join(data_dir, 'octahedron.txt')
+    convert([ply_source, txt_target])
+
+    with open(txt_target, 'r') as f:
+        lines = f.readlines()
+        assert lines == ['-1.0 1.0 0.0\n',
+                         '-1.0 -1.0 0.0\n',
+                         '1.0 -1.0 0.0\n',
+                         '1.0 1.0 0.0\n',
+                         '0.0 0.0 0.7\n',
+                         '0.0 0.0 -0.7\n']
+
+    # clean up temporary output
+    remove(txt_target)