curds: Create a single place to get a path to a data file

It's useful to have a way to override where data gets placed in the
filesystem so we don't accidentally clobber production data with test
data while running tests.

Signed-off-by: Anna Schumaker <Anna@NoWheyCreamery.com>

Makefile

@@ -8,4 +8,4 @@ clean:
 .PHONY: trier
 trier:
 	python trier/generate_tracks.py
-	python -m unittest discover -v curds/
+	EMMENTAL_TESTING=1 python -m unittest discover -v curds/

curds/data.py

@@ -0,0 +1,12 @@
+# Copyright 2019 (c) Anna Schumaker.
+import os
+import xdg.BaseDirectory
+
+__resource = "emmental"
+if os.environ.get("EMMENTAL_TESTING"):
+    __resource = "emmental-testing"
+
+emmental_data = xdg.BaseDirectory.save_data_path(__resource)
+
+def data_file_path(filename):
+    return os.path.join(emmental_data, filename)

curds/test_data.py

@@ -0,0 +1,31 @@
+# Copyright 2019 (c) Anna Schumaker.
+import data
+import os
+import unittest
+import xdg.BaseDirectory
+
+xdg_data_home = xdg.BaseDirectory.xdg_data_home
+testing_data  = os.path.join(xdg_data_home, "emmental-testing")
+
+class Test:
+    def __init__(self):
+        self.one  = 1
+        self.two  = 2
+        self.list = [ 3, 4, 5]
+
+
+class TestDataModule(unittest.TestCase):
+    def setUp(self):
+        path = os.path.join(testing_data, "test")
+        if os.path.exists(path):
+            os.remove(path)
+
+    def test_dir(self):
+        self.assertEqual(data.emmental_data, testing_data)
+        self.assertTrue(os.path.exists(testing_data))
+        self.assertTrue(os.path.isdir(testing_data))
+
+    def test_data_file_path(self):
+        path = os.path.join(testing_data, "test")
+        self.assertEqual(data.data_file_path("test"), path)
+        self.assertFalse(os.path.exists(path))