add test for layers in python

tests/python/test_File3dm_LayerTable.py

@@ -0,0 +1,36 @@
+import rhino3dm
+import unittest
+
+#objective: to test creating file with layers and reasing a file with layers
+class TestFile3dmLayerTable(unittest.TestCase):
+    def test_createFileWithLayers(self):
+
+        file3dm = rhino3dm.File3dm()
+        file3dm.ApplicationName = 'python'
+        file3dm.ApplicationDetails = 'rhino3dm-tests'
+        file3dm.ApplicationUrl = 'https://rhino3d.com'
+
+        #create layers
+        layer1 = rhino3dm.Layer()
+        layer1.Name = 'layer1'
+        layer1.Color = (255,0,255,255)
+
+        layer2 = rhino3dm.Layer()
+        layer2.Name = 'layer2'
+
+        file3dm.Layers.Add(layer1)
+        file3dm.Layers.Add(layer2)
+
+        qtyLayers = len(file3dm.Layers)
+
+        file3dm.Write('test_createFileWithLayers.3dm')
+
+        file = rhino3dm.File3dm.Read('test_createFile.3dm')
+        qtyLayers2 = len(file.Layers)
+
+        self.assertTrue(qtyLayers == qtyLayers2)
+
+if __name__ == '__main__':
+    print("running tests")
+    unittest.main()
+    print("tests complete")